diff --git a/Godeps/Godeps.json b/Godeps/Godeps.json
index f487713e7..9f5fc729a 100644
--- a/Godeps/Godeps.json
+++ b/Godeps/Godeps.json
@@ -89,6 +89,10 @@
 			"ImportPath": "github.com/inconshreveable/go-update",
 			"Rev": "221d034a558b4c21b0624b2a450c076913854a57"
 		},
+		{
+			"ImportPath": "github.com/hashicorp/golang-lru",
+			"Rev": "253b2dc1ca8bae42c3b5b6e53dd2eab1a7551116"
+		},
 		{
 			"ImportPath": "github.com/jbenet/go-base58",
 			"Rev": "568a28d73fd97651d3442392036a658b6976eed5"
diff --git a/Godeps/_workspace/src/github.com/hashicorp/golang-lru/.gitignore b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/.gitignore
new file mode 100644
index 000000000..836562412
--- /dev/null
+++ b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/.gitignore
@@ -0,0 +1,23 @@
+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+*.test
diff --git a/Godeps/_workspace/src/github.com/hashicorp/golang-lru/LICENSE b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/LICENSE
new file mode 100644
index 000000000..be2cc4dfb
--- /dev/null
+++ b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/LICENSE
@@ -0,0 +1,362 @@
+Mozilla Public License, version 2.0
+
+1. Definitions
+
+1.1. "Contributor"
+
+     means each individual or legal entity that creates, contributes to the
+     creation of, or owns Covered Software.
+
+1.2. "Contributor Version"
+
+     means the combination of the Contributions of others (if any) used by a
+     Contributor and that particular Contributor's Contribution.
+
+1.3. "Contribution"
+
+     means Covered Software of a particular Contributor.
+
+1.4. "Covered Software"
+
+     means Source Code Form to which the initial Contributor has attached the
+     notice in Exhibit A, the Executable Form of such Source Code Form, and
+     Modifications of such Source Code Form, in each case including portions
+     thereof.
+
+1.5. "Incompatible With Secondary Licenses"
+     means
+
+     a. that the initial Contributor has attached the notice described in
+        Exhibit B to the Covered Software; or
+
+     b. that the Covered Software was made available under the terms of
+        version 1.1 or earlier of the License, but not also under the terms of
+        a Secondary License.
+
+1.6. "Executable Form"
+
+     means any form of the work other than Source Code Form.
+
+1.7. "Larger Work"
+
+     means a work that combines Covered Software with other material, in a
+     separate file or files, that is not Covered Software.
+
+1.8. "License"
+
+     means this document.
+
+1.9. "Licensable"
+
+     means having the right to grant, to the maximum extent possible, whether
+     at the time of the initial grant or subsequently, any and all of the
+     rights conveyed by this License.
+
+1.10. "Modifications"
+
+     means any of the following:
+
+     a. any file in Source Code Form that results from an addition to,
+        deletion from, or modification of the contents of Covered Software; or
+
+     b. any new file in Source Code Form that contains any Covered Software.
+
+1.11. "Patent Claims" of a Contributor
+
+      means any patent claim(s), including without limitation, method,
+      process, and apparatus claims, in any patent Licensable by such
+      Contributor that would be infringed, but for the grant of the License,
+      by the making, using, selling, offering for sale, having made, import,
+      or transfer of either its Contributions or its Contributor Version.
+
+1.12. "Secondary License"
+
+      means either the GNU General Public License, Version 2.0, the GNU Lesser
+      General Public License, Version 2.1, the GNU Affero General Public
+      License, Version 3.0, or any later versions of those licenses.
+
+1.13. "Source Code Form"
+
+      means the form of the work preferred for making modifications.
+
+1.14. "You" (or "Your")
+
+      means an individual or a legal entity exercising rights under this
+      License. For legal entities, "You" includes any entity that controls, is
+      controlled by, or is under common control with You. For purposes of this
+      definition, "control" means (a) the power, direct or indirect, to cause
+      the direction or management of such entity, whether by contract or
+      otherwise, or (b) ownership of more than fifty percent (50%) of the
+      outstanding shares or beneficial ownership of such entity.
+
+
+2. License Grants and Conditions
+
+2.1. Grants
+
+     Each Contributor hereby grants You a world-wide, royalty-free,
+     non-exclusive license:
+
+     a. under intellectual property rights (other than patent or trademark)
+        Licensable by such Contributor to use, reproduce, make available,
+        modify, display, perform, distribute, and otherwise exploit its
+        Contributions, either on an unmodified basis, with Modifications, or
+        as part of a Larger Work; and
+
+     b. under Patent Claims of such Contributor to make, use, sell, offer for
+        sale, have made, import, and otherwise transfer either its
+        Contributions or its Contributor Version.
+
+2.2. Effective Date
+
+     The licenses granted in Section 2.1 with respect to any Contribution
+     become effective for each Contribution on the date the Contributor first
+     distributes such Contribution.
+
+2.3. Limitations on Grant Scope
+
+     The licenses granted in this Section 2 are the only rights granted under
+     this License. No additional rights or licenses will be implied from the
+     distribution or licensing of Covered Software under this License.
+     Notwithstanding Section 2.1(b) above, no patent license is granted by a
+     Contributor:
+
+     a. for any code that a Contributor has removed from Covered Software; or
+
+     b. for infringements caused by: (i) Your and any other third party's
+        modifications of Covered Software, or (ii) the combination of its
+        Contributions with other software (except as part of its Contributor
+        Version); or
+
+     c. under Patent Claims infringed by Covered Software in the absence of
+        its Contributions.
+
+     This License does not grant any rights in the trademarks, service marks,
+     or logos of any Contributor (except as may be necessary to comply with
+     the notice requirements in Section 3.4).
+
+2.4. Subsequent Licenses
+
+     No Contributor makes additional grants as a result of Your choice to
+     distribute the Covered Software under a subsequent version of this
+     License (see Section 10.2) or under the terms of a Secondary License (if
+     permitted under the terms of Section 3.3).
+
+2.5. Representation
+
+     Each Contributor represents that the Contributor believes its
+     Contributions are its original creation(s) or it has sufficient rights to
+     grant the rights to its Contributions conveyed by this License.
+
+2.6. Fair Use
+
+     This License is not intended to limit any rights You have under
+     applicable copyright doctrines of fair use, fair dealing, or other
+     equivalents.
+
+2.7. Conditions
+
+     Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted in
+     Section 2.1.
+
+
+3. Responsibilities
+
+3.1. Distribution of Source Form
+
+     All distribution of Covered Software in Source Code Form, including any
+     Modifications that You create or to which You contribute, must be under
+     the terms of this License. You must inform recipients that the Source
+     Code Form of the Covered Software is governed by the terms of this
+     License, and how they can obtain a copy of this License. You may not
+     attempt to alter or restrict the recipients' rights in the Source Code
+     Form.
+
+3.2. Distribution of Executable Form
+
+     If You distribute Covered Software in Executable Form then:
+
+     a. such Covered Software must also be made available in Source Code Form,
+        as described in Section 3.1, and You must inform recipients of the
+        Executable Form how they can obtain a copy of such Source Code Form by
+        reasonable means in a timely manner, at a charge no more than the cost
+        of distribution to the recipient; and
+
+     b. You may distribute such Executable Form under the terms of this
+        License, or sublicense it under different terms, provided that the
+        license for the Executable Form does not attempt to limit or alter the
+        recipients' rights in the Source Code Form under this License.
+
+3.3. Distribution of a Larger Work
+
+     You may create and distribute a Larger Work under terms of Your choice,
+     provided that You also comply with the requirements of this License for
+     the Covered Software. If the Larger Work is a combination of Covered
+     Software with a work governed by one or more Secondary Licenses, and the
+     Covered Software is not Incompatible With Secondary Licenses, this
+     License permits You to additionally distribute such Covered Software
+     under the terms of such Secondary License(s), so that the recipient of
+     the Larger Work may, at their option, further distribute the Covered
+     Software under the terms of either this License or such Secondary
+     License(s).
+
+3.4. Notices
+
+     You may not remove or alter the substance of any license notices
+     (including copyright notices, patent notices, disclaimers of warranty, or
+     limitations of liability) contained within the Source Code Form of the
+     Covered Software, except that You may alter any license notices to the
+     extent required to remedy known factual inaccuracies.
+
+3.5. Application of Additional Terms
+
+     You may choose to offer, and to charge a fee for, warranty, support,
+     indemnity or liability obligations to one or more recipients of Covered
+     Software. However, You may do so only on Your own behalf, and not on
+     behalf of any Contributor. You must make it absolutely clear that any
+     such warranty, support, indemnity, or liability obligation is offered by
+     You alone, and You hereby agree to indemnify every Contributor for any
+     liability incurred by such Contributor as a result of warranty, support,
+     indemnity or liability terms You offer. You may include additional
+     disclaimers of warranty and limitations of liability specific to any
+     jurisdiction.
+
+4. Inability to Comply Due to Statute or Regulation
+
+   If it is impossible for You to comply with any of the terms of this License
+   with respect to some or all of the Covered Software due to statute,
+   judicial order, or regulation then You must: (a) comply with the terms of
+   this License to the maximum extent possible; and (b) describe the
+   limitations and the code they affect. Such description must be placed in a
+   text file included with all distributions of the Covered Software under
+   this License. Except to the extent prohibited by statute or regulation,
+   such description must be sufficiently detailed for a recipient of ordinary
+   skill to be able to understand it.
+
+5. Termination
+
+5.1. The rights granted under this License will terminate automatically if You
+     fail to comply with any of its terms. However, if You become compliant,
+     then the rights granted under this License from a particular Contributor
+     are reinstated (a) provisionally, unless and until such Contributor
+     explicitly and finally terminates Your grants, and (b) on an ongoing
+     basis, if such Contributor fails to notify You of the non-compliance by
+     some reasonable means prior to 60 days after You have come back into
+     compliance. Moreover, Your grants from a particular Contributor are
+     reinstated on an ongoing basis if such Contributor notifies You of the
+     non-compliance by some reasonable means, this is the first time You have
+     received notice of non-compliance with this License from such
+     Contributor, and You become compliant prior to 30 days after Your receipt
+     of the notice.
+
+5.2. If You initiate litigation against any entity by asserting a patent
+     infringement claim (excluding declaratory judgment actions,
+     counter-claims, and cross-claims) alleging that a Contributor Version
+     directly or indirectly infringes any patent, then the rights granted to
+     You by any and all Contributors for the Covered Software under Section
+     2.1 of this License shall terminate.
+
+5.3. In the event of termination under Sections 5.1 or 5.2 above, all end user
+     license agreements (excluding distributors and resellers) which have been
+     validly granted by You or Your distributors under this License prior to
+     termination shall survive termination.
+
+6. Disclaimer of Warranty
+
+   Covered Software is provided under this License on an "as is" basis,
+   without warranty of any kind, either expressed, implied, or statutory,
+   including, without limitation, warranties that the Covered Software is free
+   of defects, merchantable, fit for a particular purpose or non-infringing.
+   The entire risk as to the quality and performance of the Covered Software
+   is with You. Should any Covered Software prove defective in any respect,
+   You (not any Contributor) assume the cost of any necessary servicing,
+   repair, or correction. This disclaimer of warranty constitutes an essential
+   part of this License. No use of  any Covered Software is authorized under
+   this License except under this disclaimer.
+
+7. Limitation of Liability
+
+   Under no circumstances and under no legal theory, whether tort (including
+   negligence), contract, or otherwise, shall any Contributor, or anyone who
+   distributes Covered Software as permitted above, be liable to You for any
+   direct, indirect, special, incidental, or consequential damages of any
+   character including, without limitation, damages for lost profits, loss of
+   goodwill, work stoppage, computer failure or malfunction, or any and all
+   other commercial damages or losses, even if such party shall have been
+   informed of the possibility of such damages. This limitation of liability
+   shall not apply to liability for death or personal injury resulting from
+   such party's negligence to the extent applicable law prohibits such
+   limitation. Some jurisdictions do not allow the exclusion or limitation of
+   incidental or consequential damages, so this exclusion and limitation may
+   not apply to You.
+
+8. Litigation
+
+   Any litigation relating to this License may be brought only in the courts
+   of a jurisdiction where the defendant maintains its principal place of
+   business and such litigation shall be governed by laws of that
+   jurisdiction, without reference to its conflict-of-law provisions. Nothing
+   in this Section shall prevent a party's ability to bring cross-claims or
+   counter-claims.
+
+9. Miscellaneous
+
+   This License represents the complete agreement concerning the subject
+   matter hereof. If any provision of this License is held to be
+   unenforceable, such provision shall be reformed only to the extent
+   necessary to make it enforceable. Any law or regulation which provides that
+   the language of a contract shall be construed against the drafter shall not
+   be used to construe this License against a Contributor.
+
+
+10. Versions of the License
+
+10.1. New Versions
+
+      Mozilla Foundation is the license steward. Except as provided in Section
+      10.3, no one other than the license steward has the right to modify or
+      publish new versions of this License. Each version will be given a
+      distinguishing version number.
+
+10.2. Effect of New Versions
+
+      You may distribute the Covered Software under the terms of the version
+      of the License under which You originally received the Covered Software,
+      or under the terms of any subsequent version published by the license
+      steward.
+
+10.3. Modified Versions
+
+      If you create software not governed by this License, and you want to
+      create a new license for such software, you may create and use a
+      modified version of this License if you rename the license and remove
+      any references to the name of the license steward (except to note that
+      such modified license differs from this License).
+
+10.4. Distributing Source Code Form that is Incompatible With Secondary
+      Licenses If You choose to distribute Source Code Form that is
+      Incompatible With Secondary Licenses under the terms of this version of
+      the License, the notice described in Exhibit B of this License must be
+      attached.
+
+Exhibit A - Source Code Form License Notice
+
+      This Source Code Form is subject to the
+      terms of the Mozilla Public License, v.
+      2.0. If a copy of the MPL was not
+      distributed with this file, You can
+      obtain one at
+      http://mozilla.org/MPL/2.0/.
+
+If it is not possible or desirable to put the notice in a particular file,
+then You may include the notice in a location (such as a LICENSE file in a
+relevant directory) where a recipient would be likely to look for such a
+notice.
+
+You may add additional accurate notices of copyright ownership.
+
+Exhibit B - "Incompatible With Secondary Licenses" Notice
+
+      This Source Code Form is "Incompatible
+      With Secondary Licenses", as defined by
+      the Mozilla Public License, v. 2.0.
diff --git a/Godeps/_workspace/src/github.com/hashicorp/golang-lru/README.md b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/README.md
new file mode 100644
index 000000000..37fa54d42
--- /dev/null
+++ b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/README.md
@@ -0,0 +1,25 @@
+golang-lru
+==========
+
+This provides the `lru` package which implements a fixed-size
+thread safe LRU cache. It is based on the cache in Groupcache.
+
+Documentation
+=============
+
+Full docs are available on [Godoc](http://godoc.org/github.com/hashicorp/golang-lru)
+
+Example
+=======
+
+Using the LRU is very simple:
+
+```go
+l, _ := New(128)
+for i := 0; i < 256; i++ {
+    l.Add(i, nil)
+}
+if l.Len() != 128 {
+    panic("bad len: %v", l.Len())
+}
+```
diff --git a/Godeps/_workspace/src/github.com/hashicorp/golang-lru/lru.go b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/lru.go
new file mode 100644
index 000000000..174767c54
--- /dev/null
+++ b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/lru.go
@@ -0,0 +1,134 @@
+// This package provides a simple LRU cache. It is based on the
+// LRU implementation in groupcache:
+// https://github.com/golang/groupcache/tree/master/lru
+package lru
+
+import (
+	"container/list"
+	"errors"
+	"sync"
+)
+
+// Cache is a thread-safe fixed size LRU cache.
+type Cache struct {
+	size      int
+	evictList *list.List
+	items     map[interface{}]*list.Element
+	lock      sync.Mutex
+}
+
+// entry is used to hold a value in the evictList
+type entry struct {
+	key   interface{}
+	value interface{}
+}
+
+// New creates an LRU of the given size
+func New(size int) (*Cache, error) {
+	if size <= 0 {
+		return nil, errors.New("Must provide a positive size")
+	}
+	c := &Cache{
+		size:      size,
+		evictList: list.New(),
+		items:     make(map[interface{}]*list.Element, size),
+	}
+	return c, nil
+}
+
+// Purge is used to completely clear the cache
+func (c *Cache) Purge() {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	c.evictList = list.New()
+	c.items = make(map[interface{}]*list.Element, c.size)
+}
+
+// Add adds a value to the cache.
+func (c *Cache) Add(key, value interface{}) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	// Check for existing item
+	if ent, ok := c.items[key]; ok {
+		c.evictList.MoveToFront(ent)
+		ent.Value.(*entry).value = value
+		return
+	}
+
+	// Add new item
+	ent := &entry{key, value}
+	entry := c.evictList.PushFront(ent)
+	c.items[key] = entry
+
+	// Verify size not exceeded
+	if c.evictList.Len() > c.size {
+		c.removeOldest()
+	}
+}
+
+// Get looks up a key's value from the cache.
+func (c *Cache) Get(key interface{}) (value interface{}, ok bool) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	if ent, ok := c.items[key]; ok {
+		c.evictList.MoveToFront(ent)
+		return ent.Value.(*entry).value, true
+	}
+	return
+}
+
+// Remove removes the provided key from the cache.
+func (c *Cache) Remove(key interface{}) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	if ent, ok := c.items[key]; ok {
+		c.removeElement(ent)
+	}
+}
+
+// RemoveOldest removes the oldest item from the cache.
+func (c *Cache) RemoveOldest() {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	c.removeOldest()
+}
+
+// Keys returns a slice of the keys in the cache.
+func (c *Cache) Keys() []interface{} {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	keys := make([]interface{}, len(c.items))
+	i := 0
+	for k := range c.items {
+		keys[i] = k
+		i++
+	}
+
+	return keys
+}
+
+// removeOldest removes the oldest item from the cache.
+func (c *Cache) removeOldest() {
+	ent := c.evictList.Back()
+	if ent != nil {
+		c.removeElement(ent)
+	}
+}
+
+// removeElement is used to remove a given list element from the cache
+func (c *Cache) removeElement(e *list.Element) {
+	c.evictList.Remove(e)
+	kv := e.Value.(*entry)
+	delete(c.items, kv.key)
+}
+
+// Len returns the number of items in the cache.
+func (c *Cache) Len() int {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	return c.evictList.Len()
+}
diff --git a/Godeps/_workspace/src/github.com/hashicorp/golang-lru/lru_test.go b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/lru_test.go
new file mode 100644
index 000000000..626b95fbe
--- /dev/null
+++ b/Godeps/_workspace/src/github.com/hashicorp/golang-lru/lru_test.go
@@ -0,0 +1,48 @@
+package lru
+
+import "testing"
+
+func TestLRU(t *testing.T) {
+	l, err := New(128)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	for i := 0; i < 256; i++ {
+		l.Add(i, i)
+	}
+	if l.Len() != 128 {
+		t.Fatalf("bad len: %v", l.Len())
+	}
+	for _, k := range l.Keys() {
+		if v, ok := l.Get(k); !ok || v != k {
+			t.Fatalf("bad key: %v", k)
+		}
+	}
+	for i := 0; i < 128; i++ {
+		_, ok := l.Get(i)
+		if ok {
+			t.Fatalf("should be evicted")
+		}
+	}
+	for i := 128; i < 256; i++ {
+		_, ok := l.Get(i)
+		if !ok {
+			t.Fatalf("should not be evicted")
+		}
+	}
+	for i := 128; i < 192; i++ {
+		l.Remove(i)
+		_, ok := l.Get(i)
+		if ok {
+			t.Fatalf("should be deleted")
+		}
+	}
+
+	l.Purge()
+	if l.Len() != 0 {
+		t.Fatalf("bad len: %v", l.Len())
+	}
+	if _, ok := l.Get(200); ok {
+		t.Fatalf("should contain nothing")
+	}
+}
diff --git a/blocks/blockstore/write_cache.go b/blocks/blockstore/write_cache.go
new file mode 100644
index 000000000..b46d05846
--- /dev/null
+++ b/blocks/blockstore/write_cache.go
@@ -0,0 +1,45 @@
+package blockstore
+
+import (
+	"github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/hashicorp/golang-lru"
+	"github.com/jbenet/go-ipfs/blocks"
+	u "github.com/jbenet/go-ipfs/util"
+)
+
+// WriteCached returns a blockstore that caches up to |size| unique writes (bs.Put).
+func WriteCached(bs Blockstore, size int) (Blockstore, error) {
+	c, err := lru.New(size)
+	if err != nil {
+		return nil, err
+	}
+	return &writecache{blockstore: bs, cache: c}, nil
+}
+
+type writecache struct {
+	cache      *lru.Cache // pointer b/c Cache contains a Mutex as value (complicates copying)
+	blockstore Blockstore
+}
+
+func (w *writecache) DeleteBlock(k u.Key) error {
+	w.cache.Remove(k)
+	return w.blockstore.DeleteBlock(k)
+}
+
+func (w *writecache) Has(k u.Key) (bool, error) {
+	if _, ok := w.cache.Get(k); ok {
+		return true, nil
+	}
+	return w.blockstore.Has(k)
+}
+
+func (w *writecache) Get(k u.Key) (*blocks.Block, error) {
+	return w.blockstore.Get(k)
+}
+
+func (w *writecache) Put(b *blocks.Block) error {
+	if _, ok := w.cache.Get(b.Key()); ok {
+		return nil
+	}
+	w.cache.Add(b.Key(), struct{}{})
+	return w.blockstore.Put(b)
+}
diff --git a/blocks/blockstore/write_cache_test.go b/blocks/blockstore/write_cache_test.go
new file mode 100644
index 000000000..2be865903
--- /dev/null
+++ b/blocks/blockstore/write_cache_test.go
@@ -0,0 +1,88 @@
+package blockstore
+
+import (
+	ds "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-datastore"
+	syncds "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-datastore/sync"
+	"github.com/jbenet/go-ipfs/blocks"
+	"testing"
+)
+
+func TestReturnsErrorWhenSizeNegative(t *testing.T) {
+	bs := NewBlockstore(syncds.MutexWrap(ds.NewMapDatastore()))
+	_, err := WriteCached(bs, -1)
+	if err != nil {
+		return
+	}
+	t.Fail()
+}
+
+func TestRemoveCacheEntryOnDelete(t *testing.T) {
+	b := blocks.NewBlock([]byte("foo"))
+	cd := &callbackDatastore{f: func() {}, ds: ds.NewMapDatastore()}
+	bs := NewBlockstore(syncds.MutexWrap(cd))
+	cachedbs, err := WriteCached(bs, 1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	cachedbs.Put(b)
+
+	writeHitTheDatastore := false
+	cd.SetFunc(func() {
+		writeHitTheDatastore = true
+	})
+
+	cachedbs.DeleteBlock(b.Key())
+	cachedbs.Put(b)
+	if !writeHitTheDatastore {
+		t.Fail()
+	}
+}
+
+func TestElideDuplicateWrite(t *testing.T) {
+	cd := &callbackDatastore{f: func() {}, ds: ds.NewMapDatastore()}
+	bs := NewBlockstore(syncds.MutexWrap(cd))
+	cachedbs, err := WriteCached(bs, 1)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	b1 := blocks.NewBlock([]byte("foo"))
+
+	cachedbs.Put(b1)
+	cd.SetFunc(func() {
+		t.Fatal("write hit the datastore")
+	})
+	cachedbs.Put(b1)
+}
+
+type callbackDatastore struct {
+	f  func()
+	ds ds.Datastore
+}
+
+func (c *callbackDatastore) SetFunc(f func()) { c.f = f }
+
+func (c *callbackDatastore) Put(key ds.Key, value interface{}) (err error) {
+	c.f()
+	return c.ds.Put(key, value)
+}
+
+func (c *callbackDatastore) Get(key ds.Key) (value interface{}, err error) {
+	c.f()
+	return c.ds.Get(key)
+}
+
+func (c *callbackDatastore) Has(key ds.Key) (exists bool, err error) {
+	c.f()
+	return c.ds.Has(key)
+}
+
+func (c *callbackDatastore) Delete(key ds.Key) (err error) {
+	c.f()
+	return c.ds.Delete(key)
+}
+
+func (c *callbackDatastore) KeyList() ([]ds.Key, error) {
+	c.f()
+	return c.ds.KeyList()
+}
diff --git a/blockservice/blocks_test.go b/blockservice/blocks_test.go
index 1a75723e2..2645b2024 100644
--- a/blockservice/blocks_test.go
+++ b/blockservice/blocks_test.go
@@ -19,9 +19,8 @@ import (
 )
 
 func TestBlocks(t *testing.T) {
-	d := ds.NewMapDatastore()
-	tsds := dssync.MutexWrap(d)
-	bs, err := New(blockstore.NewBlockstore(tsds), offline.Exchange())
+	bstore := blockstore.NewBlockstore(dssync.MutexWrap(ds.NewMapDatastore()))
+	bs, err := New(bstore, offline.Exchange(bstore))
 	if err != nil {
 		t.Error("failed to construct block service", err)
 		return
diff --git a/blockservice/blockservice.go b/blockservice/blockservice.go
index 0ddec7955..0ebe30a4d 100644
--- a/blockservice/blockservice.go
+++ b/blockservice/blockservice.go
@@ -25,7 +25,7 @@ var ErrNotFound = errors.New("blockservice: key not found")
 type BlockService struct {
 	// TODO don't expose underlying impl details
 	Blockstore blockstore.Blockstore
-	Remote     exchange.Interface
+	Exchange   exchange.Interface
 }
 
 // NewBlockService creates a BlockService with given datastore instance.
@@ -36,7 +36,7 @@ func New(bs blockstore.Blockstore, rem exchange.Interface) (*BlockService, error
 	if rem == nil {
 		log.Warning("blockservice running in local (offline) mode.")
 	}
-	return &BlockService{Blockstore: bs, Remote: rem}, nil
+	return &BlockService{Blockstore: bs, Exchange: rem}, nil
 }
 
 // AddBlock adds a particular block to the service, Putting it into the datastore.
@@ -66,9 +66,9 @@ func (s *BlockService) AddBlock(b *blocks.Block) (u.Key, error) {
 
 	// TODO this operation rate-limits blockservice operations, we should
 	// consider moving this to an sync process.
-	if s.Remote != nil {
+	if s.Exchange != nil {
 		ctx := context.TODO()
-		err = s.Remote.HasBlock(ctx, b)
+		err = s.Exchange.HasBlock(ctx, b)
 	}
 	return k, err
 }
@@ -82,9 +82,9 @@ func (s *BlockService) GetBlock(ctx context.Context, k u.Key) (*blocks.Block, er
 		return block, nil
 		// TODO be careful checking ErrNotFound. If the underlying
 		// implementation changes, this will break.
-	} else if err == ds.ErrNotFound && s.Remote != nil {
+	} else if err == ds.ErrNotFound && s.Exchange != nil {
 		log.Debug("Blockservice: Searching bitswap.")
-		blk, err := s.Remote.GetBlock(ctx, k)
+		blk, err := s.Exchange.GetBlock(ctx, k)
 		if err != nil {
 			return nil, err
 		}
@@ -117,7 +117,7 @@ func (s *BlockService) GetBlocks(ctx context.Context, ks []u.Key) <-chan *blocks
 			}
 		}
 
-		rblocks, err := s.Remote.GetBlocks(ctx, misses)
+		rblocks, err := s.Exchange.GetBlocks(ctx, misses)
 		if err != nil {
 			log.Errorf("Error with GetBlocks: %s", err)
 			return
diff --git a/core/core.go b/core/core.go
index 148853bfc..007c01b80 100644
--- a/core/core.go
+++ b/core/core.go
@@ -8,7 +8,7 @@ import (
 	b58 "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-base58"
 	ma "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multiaddr"
 
-	blockstore "github.com/jbenet/go-ipfs/blocks/blockstore"
+	bstore "github.com/jbenet/go-ipfs/blocks/blockstore"
 	bserv "github.com/jbenet/go-ipfs/blockservice"
 	config "github.com/jbenet/go-ipfs/config"
 	diag "github.com/jbenet/go-ipfs/diagnostics"
@@ -35,6 +35,7 @@ import (
 )
 
 const IpnsValidatorTag = "ipns"
+const kSizeBlockstoreWriteCache = 100
 
 var log = eventlog.Logger("core")
 
@@ -130,7 +131,8 @@ func NewIpfsNode(cfg *config.Config, online bool) (n *IpfsNode, err error) {
 		return nil, debugerror.Wrap(err)
 	}
 
-	n.Exchange = offline.Exchange()
+	blockstore, err := bstore.WriteCached(bstore.NewBlockstore(n.Datastore), kSizeBlockstoreWriteCache)
+	n.Exchange = offline.Exchange(blockstore)
 
 	// setup online services
 	if online {
@@ -174,16 +176,15 @@ func NewIpfsNode(cfg *config.Config, online bool) (n *IpfsNode, err error) {
 		// setup exchange service
 		const alwaysSendToPeer = true // use YesManStrategy
 		bitswapNetwork := bsnet.NewFromIpfsNetwork(exchangeService, n.Network)
-		bstore := blockstore.NewBlockstore(n.Datastore)
 
-		n.Exchange = bitswap.New(ctx, n.Identity, bitswapNetwork, n.Routing, bstore, alwaysSendToPeer)
+		n.Exchange = bitswap.New(ctx, n.Identity, bitswapNetwork, n.Routing, blockstore, alwaysSendToPeer)
 
 		go initConnections(ctx, n.Config, n.Peerstore, dhtRouting)
 	}
 
 	// TODO(brian): when offline instantiate the BlockService with a bitswap
 	// session that simply doesn't return blocks
-	n.Blocks, err = bserv.New(blockstore.NewBlockstore(n.Datastore), n.Exchange)
+	n.Blocks, err = bserv.New(blockstore, n.Exchange)
 	if err != nil {
 		return nil, debugerror.Wrap(err)
 	}
diff --git a/core/mock.go b/core/mock.go
index 2d2359277..ab1149787 100644
--- a/core/mock.go
+++ b/core/mock.go
@@ -45,7 +45,8 @@ func NewMockNode() (*IpfsNode, error) {
 	nd.Routing = dht
 
 	// Bitswap
-	bserv, err := blockservice.New(blockstore.NewBlockstore(nd.Datastore), offline.Exchange())
+	bstore := blockstore.NewBlockstore(nd.Datastore)
+	bserv, err := blockservice.New(bstore, offline.Exchange(bstore))
 	if err != nil {
 		return nil, err
 	}
diff --git a/exchange/bitswap/bitswap.go b/exchange/bitswap/bitswap.go
index e00b23f91..8dbf05314 100644
--- a/exchange/bitswap/bitswap.go
+++ b/exchange/bitswap/bitswap.go
@@ -145,6 +145,22 @@ func (bs *bitswap) GetBlocks(ctx context.Context, keys []u.Key) (<-chan *blocks.
 	}
 }
 
+// HasBlock announces the existance of a block to this bitswap service. The
+// service will potentially notify its peers.
+func (bs *bitswap) HasBlock(ctx context.Context, blk *blocks.Block) error {
+	if err := bs.blockstore.Put(blk); err != nil {
+		return err
+	}
+	bs.wantlist.Remove(blk.Key())
+	bs.notifications.Publish(blk)
+	child, _ := context.WithTimeout(ctx, hasBlockTimeout)
+	if err := bs.sendToPeersThatWant(child, blk); err != nil {
+		return err
+	}
+	child, _ = context.WithTimeout(ctx, hasBlockTimeout)
+	return bs.routing.Provide(child, blk.Key())
+}
+
 func (bs *bitswap) sendWantListTo(ctx context.Context, peers <-chan peer.Peer) error {
 	if peers == nil {
 		panic("Cant send wantlist to nil peerchan")
@@ -245,33 +261,6 @@ func (bs *bitswap) loop(parent context.Context) {
 	}
 }
 
-// HasBlock announces the existance of a block to this bitswap service. The
-// service will potentially notify its peers.
-func (bs *bitswap) HasBlock(ctx context.Context, blk *blocks.Block) error {
-	// TODO check all errors
-	log.Debugf("Has Block %s", blk.Key())
-	bs.wantlist.Remove(blk.Key())
-	bs.notifications.Publish(blk)
-
-	child, _ := context.WithTimeout(ctx, hasBlockTimeout)
-	bs.sendToPeersThatWant(child, blk)
-	child, _ = context.WithTimeout(ctx, hasBlockTimeout)
-	return bs.routing.Provide(child, blk.Key())
-}
-
-// receiveBlock handles storing the block in the blockstore and calling HasBlock
-func (bs *bitswap) receiveBlock(ctx context.Context, block *blocks.Block) {
-	// TODO verify blocks?
-	if err := bs.blockstore.Put(block); err != nil {
-		log.Criticalf("error putting block: %s", err)
-		return
-	}
-	err := bs.HasBlock(ctx, block)
-	if err != nil {
-		log.Warningf("HasBlock errored: %s", err)
-	}
-}
-
 // TODO(brian): handle errors
 func (bs *bitswap) ReceiveMessage(ctx context.Context, p peer.Peer, incoming bsmsg.BitSwapMessage) (
 	peer.Peer, bsmsg.BitSwapMessage) {
@@ -295,11 +284,11 @@ func (bs *bitswap) ReceiveMessage(ctx context.Context, p peer.Peer, incoming bsm
 	// and number of bytes transfered.
 	bs.strategy.MessageReceived(p, incoming)
 
-	go func() {
-		for _, block := range incoming.Blocks() {
-			bs.receiveBlock(ctx, block)
+	for _, block := range incoming.Blocks() {
+		if err := bs.HasBlock(ctx, block); err != nil {
+			log.Error(err)
 		}
-	}()
+	}
 
 	for _, key := range incoming.Wantlist() {
 		if bs.strategy.ShouldSendBlockToPeer(key, p) {
@@ -334,27 +323,29 @@ func (bs *bitswap) ReceiveError(err error) {
 
 // send strives to ensure that accounting is always performed when a message is
 // sent
-func (bs *bitswap) send(ctx context.Context, p peer.Peer, m bsmsg.BitSwapMessage) {
-	bs.sender.SendMessage(ctx, p, m)
-	bs.strategy.MessageSent(p, m)
+func (bs *bitswap) send(ctx context.Context, p peer.Peer, m bsmsg.BitSwapMessage) error {
+	if err := bs.sender.SendMessage(ctx, p, m); err != nil {
+		return err
+	}
+	return bs.strategy.MessageSent(p, m)
 }
 
-func (bs *bitswap) sendToPeersThatWant(ctx context.Context, block *blocks.Block) {
-	log.Debugf("Sending %s to peers that want it", block)
-
+func (bs *bitswap) sendToPeersThatWant(ctx context.Context, block *blocks.Block) error {
 	for _, p := range bs.strategy.Peers() {
 		if bs.strategy.BlockIsWantedByPeer(block.Key(), p) {
-			log.Debugf("%v wants %v", p, block.Key())
 			if bs.strategy.ShouldSendBlockToPeer(block.Key(), p) {
 				message := bsmsg.New()
 				message.AddBlock(block)
 				for _, wanted := range bs.wantlist.Keys() {
 					message.AddWanted(wanted)
 				}
-				bs.send(ctx, p, message)
+				if err := bs.send(ctx, p, message); err != nil {
+					return err
+				}
 			}
 		}
 	}
+	return nil
 }
 
 func (bs *bitswap) Close() error {
diff --git a/exchange/offline/offline.go b/exchange/offline/offline.go
index 24a89e038..f1a6aaa61 100644
--- a/exchange/offline/offline.go
+++ b/exchange/offline/offline.go
@@ -3,42 +3,66 @@
 package offline
 
 import (
-	"errors"
-
 	context "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/go.net/context"
-
 	blocks "github.com/jbenet/go-ipfs/blocks"
+	"github.com/jbenet/go-ipfs/blocks/blockstore"
 	exchange "github.com/jbenet/go-ipfs/exchange"
 	u "github.com/jbenet/go-ipfs/util"
 )
 
-var OfflineMode = errors.New("Block unavailable. Operating in offline mode")
-
-func Exchange() exchange.Interface {
-	return &offlineExchange{}
+func Exchange(bs blockstore.Blockstore) exchange.Interface {
+	return &offlineExchange{bs: bs}
 }
 
 // offlineExchange implements the Exchange interface but doesn't return blocks.
 // For use in offline mode.
-type offlineExchange struct{}
+type offlineExchange struct {
+	bs blockstore.Blockstore
+}
 
 // GetBlock returns nil to signal that a block could not be retrieved for the
 // given key.
 // NB: This function may return before the timeout expires.
-func (_ *offlineExchange) GetBlock(context.Context, u.Key) (*blocks.Block, error) {
-	return nil, OfflineMode
+func (e *offlineExchange) GetBlock(_ context.Context, k u.Key) (*blocks.Block, error) {
+	return e.bs.Get(k)
 }
 
 // HasBlock always returns nil.
-func (_ *offlineExchange) HasBlock(context.Context, *blocks.Block) error {
-	return nil
+func (e *offlineExchange) HasBlock(_ context.Context, b *blocks.Block) error {
+	return e.bs.Put(b)
 }
 
 // Close always returns nil.
 func (_ *offlineExchange) Close() error {
+	// NB: exchange doesn't own the blockstore's underlying datastore, so it is
+	// not responsible for closing it.
 	return nil
 }
 
-func (_ *offlineExchange) GetBlocks(context.Context, []u.Key) (<-chan *blocks.Block, error) {
-	return nil, OfflineMode
+func (e *offlineExchange) GetBlocks(ctx context.Context, ks []u.Key) (<-chan *blocks.Block, error) {
+	out := make(chan *blocks.Block, 0)
+	go func() {
+		defer close(out)
+		var misses []u.Key
+		for _, k := range ks {
+			hit, err := e.bs.Get(k)
+			if err != nil {
+				misses = append(misses, k)
+				// a long line of misses should abort when context is cancelled.
+				select {
+				// TODO case send misses down channel
+				case <-ctx.Done():
+					return
+				default:
+					continue
+				}
+			}
+			select {
+			case out <- hit:
+			case <-ctx.Done():
+				return
+			}
+		}
+	}()
+	return out, nil
 }
diff --git a/exchange/offline/offline_test.go b/exchange/offline/offline_test.go
index ac02d2101..d32f336d0 100644
--- a/exchange/offline/offline_test.go
+++ b/exchange/offline/offline_test.go
@@ -4,13 +4,16 @@ import (
 	"testing"
 
 	context "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/go.net/context"
-
+	ds "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-datastore"
+	ds_sync "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-datastore/sync"
 	blocks "github.com/jbenet/go-ipfs/blocks"
+	"github.com/jbenet/go-ipfs/blocks/blockstore"
+	"github.com/jbenet/go-ipfs/blocks/blocksutil"
 	u "github.com/jbenet/go-ipfs/util"
 )
 
 func TestBlockReturnsErr(t *testing.T) {
-	off := Exchange()
+	off := Exchange(bstore())
 	_, err := off.GetBlock(context.Background(), u.Key("foo"))
 	if err != nil {
 		return // as desired
@@ -19,10 +22,56 @@ func TestBlockReturnsErr(t *testing.T) {
 }
 
 func TestHasBlockReturnsNil(t *testing.T) {
-	off := Exchange()
+	store := bstore()
+	ex := Exchange(store)
 	block := blocks.NewBlock([]byte("data"))
-	err := off.HasBlock(context.Background(), block)
+
+	err := ex.HasBlock(context.Background(), block)
 	if err != nil {
-		t.Fatal("")
+		t.Fail()
+	}
+
+	if _, err := store.Get(block.Key()); err != nil {
+		t.Fatal(err)
 	}
 }
+
+func TestGetBlocks(t *testing.T) {
+	store := bstore()
+	ex := Exchange(store)
+	g := blocksutil.NewBlockGenerator()
+
+	expected := g.Blocks(2)
+
+	for _, b := range expected {
+		if err := ex.HasBlock(context.Background(), b); err != nil {
+			t.Fail()
+		}
+	}
+
+	request := func() []u.Key {
+		var ks []u.Key
+
+		for _, b := range expected {
+			ks = append(ks, b.Key())
+		}
+		return ks
+	}()
+
+	received, err := ex.GetBlocks(context.Background(), request)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var count int
+	for _ = range received {
+		count++
+	}
+	if len(expected) != count {
+		t.Fail()
+	}
+}
+
+func bstore() blockstore.Blockstore {
+	return blockstore.NewBlockstore(ds_sync.MutexWrap(ds.NewMapDatastore()))
+}
diff --git a/pin/pin_test.go b/pin/pin_test.go
index fc9dc215d..dada99803 100644
--- a/pin/pin_test.go
+++ b/pin/pin_test.go
@@ -23,7 +23,7 @@ func randNode() (*mdag.Node, util.Key) {
 func TestPinnerBasic(t *testing.T) {
 	dstore := ds.NewMapDatastore()
 	bstore := blockstore.NewBlockstore(dssync.MutexWrap(dstore))
-	bserv, err := bs.New(bstore, offline.Exchange())
+	bserv, err := bs.New(bstore, offline.Exchange(bstore))
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/routing/dht/providers.go b/routing/dht/providers.go
index 7f70056d3..0deea6324 100644
--- a/routing/dht/providers.go
+++ b/routing/dht/providers.go
@@ -107,10 +107,15 @@ func (pm *ProviderManager) GetProviders(ctx context.Context, k u.Key) []peer.Pee
 		resp: make(chan []peer.Peer, 1), // buffered to prevent sender from blocking
 	}
 	select {
-	case pm.getprovs <- gp:
-		return <-gp.resp
 	case <-ctx.Done():
 		return nil
+	case pm.getprovs <- gp:
+	}
+	select {
+	case <-ctx.Done():
+		return nil
+	case peers := <-gp.resp:
+		return peers
 	}
 }
 
diff --git a/unixfs/io/dagmodifier_test.go b/unixfs/io/dagmodifier_test.go
index d0aa83795..ed5b10d69 100644
--- a/unixfs/io/dagmodifier_test.go
+++ b/unixfs/io/dagmodifier_test.go
@@ -24,7 +24,7 @@ func getMockDagServ(t *testing.T) mdag.DAGService {
 	dstore := ds.NewMapDatastore()
 	tsds := sync.MutexWrap(dstore)
 	bstore := blockstore.NewBlockstore(tsds)
-	bserv, err := bs.New(bstore, offline.Exchange())
+	bserv, err := bs.New(bstore, offline.Exchange(bstore))
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/util/testutil/gen.go b/util/testutil/gen.go
index c7f310c2a..186740ea9 100644
--- a/util/testutil/gen.go
+++ b/util/testutil/gen.go
@@ -16,9 +16,8 @@ import (
 )
 
 func GetDAGServ(t testing.TB) dag.DAGService {
-	dstore := ds.NewMapDatastore()
-	tsds := dssync.MutexWrap(dstore)
-	bserv, err := bsrv.New(blockstore.NewBlockstore(tsds), offline.Exchange())
+	bstore := blockstore.NewBlockstore(dssync.MutexWrap(ds.NewMapDatastore()))
+	bserv, err := bsrv.New(bstore, offline.Exchange(bstore))
 	if err != nil {
 		t.Fatal(err)
 	}