diff --git a/fs.go b/fs.go
index 8415f4795..cdc33fb8e 100644
--- a/fs.go
+++ b/fs.go
@@ -3,12 +3,15 @@
 package main
 
 import (
+	"fmt"
 	"io"
+	"log"
 	"time"
 )
 
 // A Filesystem, describes the local filesystem and the remote object store
 type Fs interface {
+	String() string
 	List() FsObjectsChan
 	NewFsObject(remote string) FsObject
 	Put(src FsObject)
@@ -22,7 +25,6 @@ type Fs interface {
 // local file/directory
 type FsObject interface {
 	Remote() string
-	Debugf(string, ...interface{})
 	Md5sum() (string, error)
 	ModTime() (time.Time, error)
 	SetModTime(time.Time)
@@ -47,6 +49,22 @@ func NewFs(path string) (Fs, error) {
 	return NewFsLocal(path)
 }
 
+// Write debuging output for this FsObject
+func FsDebug(fs FsObject, text string, args ...interface{}) {
+	if *verbose {
+		out := fmt.Sprintf(text, args...)
+		log.Printf("%s: %s", fs.Remote(), out)
+	}
+}
+
+// Write log output for this FsObject
+func FsLog(fs FsObject, text string, args ...interface{}) {
+	if !*quiet {
+		out := fmt.Sprintf(text, args...)
+		log.Printf("%s: %s", fs.Remote(), out)
+	}
+}
+
 // checkClose is a utility function used to check the return from
 // Close in a defer statement.
 func checkClose(c io.Closer, err *error) {
@@ -74,22 +92,22 @@ func checkClose(c io.Closer, err *error) {
 // were errors reading info.
 func Equal(src, dst FsObject) bool {
 	if src.Size() != dst.Size() {
-		src.Debugf("Sizes differ")
+		FsDebug(src, "Sizes differ")
 		return false
 	}
 
 	// Size the same so check the mtime
 	srcModTime, err := src.ModTime()
 	if err != nil {
-		src.Debugf("Failed to read src mtime: %s", err)
+		FsDebug(src, "Failed to read src mtime: %s", err)
 	} else {
 		dstModTime, err := dst.ModTime()
 		if err != nil {
-			dst.Debugf("Failed to read dst mtime: %s", err)
+			FsDebug(dst, "Failed to read dst mtime: %s", err)
 		} else if !dstModTime.Equal(srcModTime) {
-			src.Debugf("Modification times differ")
+			FsDebug(src, "Modification times differ")
 		} else {
-			src.Debugf("Size and modification time the same")
+			FsDebug(src, "Size and modification time the same")
 			return true
 		}
 	}
@@ -98,18 +116,18 @@ func Equal(src, dst FsObject) bool {
 	// check the MD5SUM
 	srcMd5, err := src.Md5sum()
 	if err != nil {
-		src.Debugf("Failed to calculate src md5: %s", err)
+		FsDebug(src, "Failed to calculate src md5: %s", err)
 		return false
 	}
 	dstMd5, err := dst.Md5sum()
 	if err != nil {
-		dst.Debugf("Failed to calculate dst md5: %s", err)
+		FsDebug(dst, "Failed to calculate dst md5: %s", err)
 		return false
 	}
-	// fs.Debugf("Src MD5 %s", srcMd5)
-	// fs.Debugf("Dst MD5 %s", obj.Hash)
+	// FsDebug("Src MD5 %s", srcMd5)
+	// FsDebug("Dst MD5 %s", obj.Hash)
 	if srcMd5 != dstMd5 {
-		src.Debugf("Md5sums differ")
+		FsDebug(src, "Md5sums differ")
 		return false
 	}
 
@@ -117,6 +135,6 @@ func Equal(src, dst FsObject) bool {
 	// mtime of the dst object here
 	dst.SetModTime(srcModTime)
 
-	src.Debugf("Size and MD5SUM of src and dst objects identical")
+	FsDebug(src, "Size and MD5SUM of src and dst objects identical")
 	return true
 }
diff --git a/fs_local.go b/fs_local.go
index 84f0440bd..7d36924e9 100644
--- a/fs_local.go
+++ b/fs_local.go
@@ -33,6 +33,11 @@ func NewFsLocal(root string) (*FsLocal, error) {
 	return f, nil
 }
 
+// String converts this FsLocal to a string
+func (f *FsLocal) String() string {
+	return fmt.Sprintf("Local file system at %s", f.root)
+}
+
 // Return an FsObject from a path
 //
 // May return nil if an error occurred
@@ -109,13 +114,13 @@ func (f *FsLocal) Put(src FsObject) {
 	dir := path.Dir(dstPath)
 	err := os.MkdirAll(dir, 0770)
 	if err != nil {
-		fs.Debugf("Couldn't make directory: %s", err)
+		FsLog(fs, "Couldn't make directory: %s", err)
 		return
 	}
 
 	out, err := os.Create(dstPath)
 	if err != nil {
-		fs.Debugf("Failed to open: %s", err)
+		FsLog(fs, "Failed to open: %s", err)
 		return
 	}
 
@@ -123,31 +128,31 @@ func (f *FsLocal) Put(src FsObject) {
 	defer func() {
 		checkClose(out, &err)
 		if err != nil {
-			fs.Debugf("Removing failed download")
+			FsDebug(fs, "Removing failed download")
 			removeErr := os.Remove(dstPath)
 			if removeErr != nil {
-				fs.Debugf("Failed to remove failed download: %s", err)
+				FsLog(fs, "Failed to remove failed download: %s", err)
 			}
 		}
 	}()
 
 	in, err := src.Open()
 	if err != nil {
-		fs.Debugf("Failed to open: %s", err)
+		FsLog(fs, "Failed to open: %s", err)
 		return
 	}
 	defer checkClose(in, &err)
 
 	_, err = io.Copy(out, in)
 	if err != nil {
-		fs.Debugf("Failed to download: %s", err)
+		FsLog(fs, "Failed to download: %s", err)
 		return
 	}
 
 	// Set the mtime
 	modTime, err := src.ModTime()
 	if err != nil {
-		fs.Debugf("Failed to read mtime from object: %s", err)
+		FsDebug(fs, "Failed to read mtime from object: %s", err)
 	} else {
 		fs.SetModTime(modTime)
 	}
@@ -172,24 +177,18 @@ func (fs *FsObjectLocal) Remote() string {
 	return fs.remote
 }
 
-// Write debuging output for this FsObject
-func (fs *FsObjectLocal) Debugf(text string, args ...interface{}) {
-	out := fmt.Sprintf(text, args...)
-	log.Printf("%s: %s", fs.remote, out)
-}
-
 // Md5sum calculates the Md5sum of a file returning a lowercase hex string
 func (fs *FsObjectLocal) Md5sum() (string, error) {
 	in, err := os.Open(fs.path)
 	if err != nil {
-		fs.Debugf("Failed to open: %s", err)
+		FsLog(fs, "Failed to open: %s", err)
 		return "", err
 	}
 	defer in.Close() // FIXME ignoring error
 	hash := md5.New()
 	_, err = io.Copy(hash, in)
 	if err != nil {
-		fs.Debugf("Failed to read: %s", err)
+		FsLog(fs, "Failed to read: %s", err)
 		return "", err
 	}
 	return fmt.Sprintf("%x", hash.Sum(nil)), nil
@@ -209,7 +208,7 @@ func (fs *FsObjectLocal) ModTime() (modTime time.Time, err error) {
 func (fs *FsObjectLocal) SetModTime(modTime time.Time) {
 	err := Chtimes(fs.path, modTime, modTime)
 	if err != nil {
-		fs.Debugf("Failed to set mtime on file: %s", err)
+		FsDebug(fs, "Failed to set mtime on file: %s", err)
 	}
 }
 
@@ -217,11 +216,10 @@ func (fs *FsObjectLocal) SetModTime(modTime time.Time) {
 func (fs *FsObjectLocal) Storable() bool {
 	mode := fs.info.Mode()
 	if mode&(os.ModeSymlink|os.ModeNamedPipe|os.ModeSocket|os.ModeDevice) != 0 {
-		fs.Debugf("Can't transfer non file/directory")
+		FsDebug(fs, "Can't transfer non file/directory")
 		return false
 	} else if mode&os.ModeDir != 0 {
-		// Debug?
-		fs.Debugf("FIXME Skipping directory")
+		FsDebug(fs, "FIXME Skipping directory")
 		return false
 	}
 	return true
diff --git a/fs_swift.go b/fs_swift.go
index 2b8776e65..91883403d 100644
--- a/fs_swift.go
+++ b/fs_swift.go
@@ -41,6 +41,11 @@ var (
 	apiKey   = flag.String("key", os.Getenv("ST_KEY"), "API key (password). Defaults to environment var ST_KEY.")
 )
 
+// String converts this FsSwift to a string
+func (f *FsSwift) String() string {
+	return fmt.Sprintf("Swift container %s", f.container)
+}
+
 // Pattern to match a swift url
 var swiftMatch = regexp.MustCompile(`^([^/:]+):(.*)$`)
 
@@ -125,7 +130,7 @@ func (f *FsSwift) NewFsObjectWithInfo(remote string, info *swift.Object) FsObjec
 	} else {
 		err := fs.readMetaData() // reads info and meta, returning an error
 		if err != nil {
-			// logged already fs.Debugf("Failed to read info: %s", err)
+			// logged already FsDebug("Failed to read info: %s", err)
 			return nil
 		}
 	}
@@ -171,7 +176,7 @@ func (f *FsSwift) Put(src FsObject) {
 	// FIXME content type
 	in, err := src.Open()
 	if err != nil {
-		fs.Debugf("Failed to open: %s", err)
+		FsLog(fs, "Failed to open: %s", err)
 		return
 	}
 	defer in.Close()
@@ -180,17 +185,17 @@ func (f *FsSwift) Put(src FsObject) {
 	m := swift.Metadata{}
 	modTime, err := src.ModTime()
 	if err != nil {
-		fs.Debugf("Failed to read mtime from object: %s", err)
+		FsDebug(fs, "Failed to read mtime from object: %s", err)
 	} else {
 		m.SetModTime(modTime)
 	}
 
 	_, err = fs.swift.c.ObjectPut(fs.swift.container, fs.remote, in, true, "", "", m.ObjectHeaders())
 	if err != nil {
-		fs.Debugf("Failed to upload: %s", err)
+		FsLog(fs, "Failed to upload: %s", err)
 		return
 	}
-	fs.Debugf("Uploaded")
+	FsDebug(fs, "Uploaded")
 }
 
 // Mkdir creates the container if it doesn't exist
@@ -212,12 +217,6 @@ func (fs *FsObjectSwift) Remote() string {
 	return fs.remote
 }
 
-// Write debuging output for this FsObject
-func (fs *FsObjectSwift) Debugf(text string, args ...interface{}) {
-	out := fmt.Sprintf(text, args...)
-	log.Printf("%s: %s", fs.remote, out)
-}
-
 // Md5sum returns the Md5sum of an object returning a lowercase hex string
 func (fs *FsObjectSwift) Md5sum() (string, error) {
 	return strings.ToLower(fs.info.Hash), nil
@@ -237,7 +236,7 @@ func (fs *FsObjectSwift) readMetaData() (err error) {
 	}
 	info, h, err := fs.swift.c.Object(fs.swift.container, fs.remote)
 	if err != nil {
-		fs.Debugf("Failed to read info: %s", err)
+		FsLog(fs, "Failed to read info: %s", err)
 		return err
 	}
 	meta := h.ObjectMetadata()
@@ -250,12 +249,12 @@ func (fs *FsObjectSwift) readMetaData() (err error) {
 func (fs *FsObjectSwift) ModTime() (modTime time.Time, err error) {
 	err = fs.readMetaData()
 	if err != nil {
-		fs.Debugf("Failed to read metadata: %s", err)
+		FsLog(fs, "Failed to read metadata: %s", err)
 		return
 	}
 	modTime, err = fs.meta.GetModTime()
 	if err != nil {
-		fs.Debugf("Failed to read mtime from object: %s", err)
+		FsLog(fs, "Failed to read mtime from object: %s", err)
 		return
 	}
 	return
@@ -265,13 +264,13 @@ func (fs *FsObjectSwift) ModTime() (modTime time.Time, err error) {
 func (fs *FsObjectSwift) SetModTime(modTime time.Time) {
 	err := fs.readMetaData()
 	if err != nil {
-		fs.Debugf("Failed to read metadata: %s", err)
+		FsLog(fs, "Failed to read metadata: %s", err)
 		return
 	}
 	fs.meta.SetModTime(modTime)
 	err = fs.swift.c.ObjectUpdate(fs.swift.container, fs.remote, fs.meta.ObjectHeaders())
 	if err != nil {
-		fs.Debugf("Failed to update remote mtime: %s", err)
+		FsLog(fs, "Failed to update remote mtime: %s", err)
 	}
 }
 
diff --git a/notes.txt b/notes.txt
index d3c1f3b2d..c93cd0adc 100644
--- a/notes.txt
+++ b/notes.txt
@@ -1,17 +1,18 @@
 Todo
-  * Add sync command (like rsync with delete)
   * Check logging in various parts
-  * Make logging controllable with flags
+  * Make logging controllable with flags (mostly done)
   * progress meter would be nice! Do this by wrapping the Reader with a progress bar
   * Do bandwidth limit by wrapping the Reader too
       * Maybe using https://jra-go.googlecode.com/hg/linkio/ which will work for multiple
         uploads or downloads. 
       * code.google.com/p/mxk/go1/flowcontrol - only does one flow at once
       * Or maybe put into swift library.
-  * Make swift timeouts be settable with command line parameters
+  * -timeout: Make all timeouts be settable with command line parameters
   * Check the locking in swift module!
   * Windows paths? Do we need to translate / and \?
   * Make a fs.Errorf and count errors and log them at a different level
+  * add -modify-window flag - fs should keep knowledge of resolution
+  * add check command to compare local MD5SUMs with remote
 
 Ideas
   * optimise remote copy container to another container using remote
diff --git a/swiftsync.go b/swiftsync.go
index 1daffc4fe..3da76f94e 100644
--- a/swiftsync.go
+++ b/swiftsync.go
@@ -21,6 +21,7 @@ var (
 	snet       = flag.Bool("snet", false, "Use internal service network") // FIXME not implemented
 	verbose    = flag.Bool("verbose", false, "Print lots more stuff")
 	quiet      = flag.Bool("quiet", false, "Print as little stuff as possible")
+	dry_run    = flag.Bool("dry-run", false, "Do a trial run with no permanent changes")
 	checkers   = flag.Int("checkers", 8, "Number of checkers to run in parallel.")
 	transfers  = flag.Int("transfers", 4, "Number of file transfers to run in parallel.")
 )
@@ -33,7 +34,7 @@ func Checker(in, out FsObjectsChan, fdst Fs, wg *sync.WaitGroup) {
 	for src := range in {
 		dst := fdst.NewFsObject(src.Remote())
 		if dst == nil {
-			src.Debugf("Couldn't find local file - download")
+			FsDebug(src, "Couldn't find local file - download")
 			out <- src
 			continue
 		}
@@ -44,7 +45,7 @@ func Checker(in, out FsObjectsChan, fdst Fs, wg *sync.WaitGroup) {
 		}
 		// Check to see if changed or not
 		if Equal(src, dst) {
-			src.Debugf("Unchanged skipping")
+			FsDebug(src, "Unchanged skipping")
 			continue
 		}
 		out <- src
@@ -88,9 +89,87 @@ func Copy(fdst, fsrc Fs) {
 	copierWg.Wait()
 }
 
-// Copy~s from source to dest
-func copy_(fdst, fsrc Fs) {
-	Copy(fdst, fsrc)
+// Delete all the files passed in the channel
+func DeleteFiles(to_be_deleted FsObjectsChan) {
+	var wg sync.WaitGroup
+	wg.Add(*transfers)
+	for i := 0; i < *transfers; i++ {
+		go func() {
+			defer wg.Done()
+			for dst := range to_be_deleted {
+				if *dry_run {
+					FsDebug(dst, "Not deleting as -dry-run")
+				} else {
+					err := dst.Remove()
+					if err != nil {
+						FsLog(dst, "Couldn't delete: %s", err)
+					} else {
+						FsDebug(dst, "Deleted")
+					}
+				}
+			}
+		}()
+	}
+
+	log.Printf("Waiting for deletions to finish")
+	wg.Wait()
+}
+
+// Syncs fsrc into fdst
+func Sync(fdst, fsrc Fs) {
+	err := fdst.Mkdir()
+	if err != nil {
+		log.Fatal("Failed to make destination")
+	}
+
+	// Read the destination files first
+	// FIXME could do this in parallel and make it use less memory
+	delFiles := make(map[string]FsObject)
+	for dstFile := range fdst.List() {
+		delFiles[dstFile.Remote()] = dstFile
+	}
+
+	// Read source files checking them off against dest files
+	to_be_checked := make(FsObjectsChan, *transfers)
+	go func() {
+		for srcFile := range fsrc.List() {
+			delete(delFiles, srcFile.Remote())
+			to_be_checked <- srcFile
+		}
+		close(to_be_checked)
+	}()
+
+	to_be_uploaded := make(FsObjectsChan, *transfers)
+
+	var checkerWg sync.WaitGroup
+	checkerWg.Add(*checkers)
+	for i := 0; i < *checkers; i++ {
+		go Checker(to_be_checked, to_be_uploaded, fdst, &checkerWg)
+	}
+
+	var copierWg sync.WaitGroup
+	copierWg.Add(*transfers)
+	for i := 0; i < *transfers; i++ {
+		go Copier(to_be_uploaded, fdst, &copierWg)
+	}
+
+	log.Printf("Waiting for checks to finish")
+	checkerWg.Wait()
+	close(to_be_uploaded)
+	log.Printf("Waiting for transfers to finish")
+	copierWg.Wait()
+
+	// FIXME don't delete if IO errors
+
+	// Delete the spare files
+	toDelete := make(FsObjectsChan, *transfers)
+	go func() {
+		for _, fs := range delFiles {
+			toDelete <- fs
+		}
+		close(toDelete)
+	}()
+	DeleteFiles(toDelete)
 }
 
 // List the Fs to stdout
@@ -129,9 +208,13 @@ func mkdir(fdst, fsrc Fs) {
 
 // Removes a container but not if not empty
 func rmdir(fdst, fsrc Fs) {
-	err := fdst.Rmdir()
-	if err != nil {
-		log.Fatalf("Rmdir failed: %s", err)
+	if *dry_run {
+		log.Printf("Not deleting %s as -dry-run", fdst)
+	} else {
+		err := fdst.Rmdir()
+		if err != nil {
+			log.Fatalf("Rmdir failed: %s", err)
+		}
 	}
 }
 
@@ -139,27 +222,7 @@ func rmdir(fdst, fsrc Fs) {
 //
 // FIXME doesn't delete local directories
 func purge(fdst, fsrc Fs) {
-	to_be_deleted := fdst.List()
-
-	var wg sync.WaitGroup
-	wg.Add(*transfers)
-	for i := 0; i < *transfers; i++ {
-		go func() {
-			defer wg.Done()
-			for dst := range to_be_deleted {
-				err := dst.Remove()
-				if err != nil {
-					log.Printf("%s: Couldn't delete: %s\n", dst.Remote(), err)
-				} else {
-					log.Printf("%s: Deleted\n", dst.Remote())
-				}
-			}
-		}()
-	}
-
-	log.Printf("Waiting for deletions to finish")
-	wg.Wait()
-
+	DeleteFiles(fdst.List())
 	log.Printf("Deleting path")
 	rmdir(fdst, fsrc)
 }
@@ -194,7 +257,21 @@ var Commands = []Command{
         MD5SUM.  Doesn't delete files from the destination.
 
 `,
-		copy_,
+		Copy,
+		2, 2,
+	},
+	{
+		"sync",
+		`<source> <destination>
+
+        Sync the source to the destination.  Doesn't transfer
+        unchanged files, testing first by modification time then by
+        MD5SUM.  Deletes any files that exist in source that don't
+        exist in destination. Since this can cause data loss, test
+        first with the -dry-run flag.
+
+`,
+		Sync,
 		2, 2,
 	},
 	{