diff --git a/Backend/Hash.hs b/Backend/Hash.hs
index f55fa68994..ec478890fb 100644
--- a/Backend/Hash.hs
+++ b/Backend/Hash.hs
@@ -124,7 +124,7 @@ checkKeyChecksum hash key file = catchIOErrorType HardwareFault hwfault $ do
 	exists <- liftIO $ R.doesPathExist file
 	case (exists, fast) of
 		(True, False) -> do
-			showAction "checksum"
+			showAction descChecksum
 			sameCheckSum key 
 				<$> hashFile hash file nullMeterUpdate
 		_ -> return True
@@ -293,8 +293,12 @@ mkIncrementalVerifier ctx key = do
 					return $ sameCheckSum key (show digest)
 				Nothing -> return False
 		, failIncremental = writeIORef v Nothing
+		, descVerify = descChecksum
 		}
 
+descChecksum :: String
+descChecksum = "checksum"
+
 {- A varient of the SHA256E backend, for testing that needs special keys
  - that cannot collide with legitimate keys in the repository.
  -
diff --git a/CHANGELOG b/CHANGELOG
index 60e29e662f..0b06cf8235 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -8,9 +8,10 @@ git-annex (8.20210804) UNRELEASED; urgency=medium
   * add: When adding a dotfile, avoid treating its name as an extension.
   * rsync special remote: Stop displaying rsync progress, and use
     git-annex's own progress display.
-  * Several special remotes verify content while it is being retrieved,
-    avoiding a separate checksum pass. They are: S3, bup, ddar,
-    and gcrypt (with a local repository).
+  * Special remotes now checksum content while it is being retrieved,
+    instead of in a separate pass at the end. This is supported for all
+    special remotes on Linux (except for web and bittorrent), and for a
+    few on other OSs (S3, bup, ddar, gcrypt).
 
  -- Joey Hess <id@joeyh.name>  Tue, 03 Aug 2021 12:22:45 -0400
 
diff --git a/Remote/Directory/LegacyChunked.hs b/Remote/Directory/LegacyChunked.hs
index cf02ca1285..42a94f8d02 100644
--- a/Remote/Directory/LegacyChunked.hs
+++ b/Remote/Directory/LegacyChunked.hs
@@ -98,7 +98,7 @@ store repotop chunksize finalizer k b p = storeHelper repotop finalizer k $ \des
  - :/ This is legacy code..
  -}
 retrieve :: (RawFilePath -> Key -> [RawFilePath]) -> RawFilePath -> Retriever
-retrieve locations d basek p c = withOtherTmp $ \tmpdir -> do
+retrieve locations d basek p miv c = withOtherTmp $ \tmpdir -> do
 	showLongNote "This remote uses the deprecated chunksize setting. So this will be quite slow."
 	let tmp = tmpdir P.</> keyFile basek <> ".directorylegacy.tmp"
 	let tmp' = fromRawFilePath tmp
@@ -110,7 +110,7 @@ retrieve locations d basek p c = withOtherTmp $ \tmpdir -> do
 		b <- liftIO $ L.readFile tmp'
 		liftIO $ removeWhenExistsWith R.removeLink tmp
 		sink b
-	byteRetriever go basek p c
+	byteRetriever go basek p miv c
 
 checkKey :: RawFilePath -> (RawFilePath -> Key -> [RawFilePath]) -> Key -> Annex Bool
 checkKey d locations k = liftIO $
diff --git a/Remote/GCrypt.hs b/Remote/GCrypt.hs
index 75002cb190..f2b3efe98c 100644
--- a/Remote/GCrypt.hs
+++ b/Remote/GCrypt.hs
@@ -407,9 +407,9 @@ store' repo r rsyncopts accessmethod
 	storersync = fileStorer $ Remote.Rsync.store rsyncopts
 
 retrieve :: Remote -> Remote.Rsync.RsyncOpts -> AccessMethod -> Retriever
-retrieve r rsyncopts accessmethod k p sink = do
+retrieve r rsyncopts accessmethod k p miv sink = do
 	repo <- getRepo r
-	retrieve' repo r rsyncopts accessmethod k p sink
+	retrieve' repo r rsyncopts accessmethod k p miv sink
 
 retrieve' :: Git.Repo -> Remote -> Remote.Rsync.RsyncOpts -> AccessMethod -> Retriever
 retrieve' repo r rsyncopts accessmethod
diff --git a/Remote/Helper/Chunked.hs b/Remote/Helper/Chunked.hs
index 56271df5ac..a810557c83 100644
--- a/Remote/Helper/Chunked.hs
+++ b/Remote/Helper/Chunked.hs
@@ -267,8 +267,7 @@ retrieveChunks retriever u vc chunkconfig encryptor basek dest basep enc encc
 		-- Optimisation: Try the unchunked key first, to avoid
 		-- looking in the git-annex branch for chunk counts
 		-- that are likely not there.
-		iv <- startVerifyKeyContentIncrementally vc basek
-		tryNonAsync (getunchunked iv) >>= \case
+		tryNonAsync getunchunked >>= \case
 			Right r -> finalize r
 			Left e -> go (Just e) 
 				=<< chunkKeysOnly u chunkconfig basek
@@ -287,22 +286,20 @@ retrieveChunks retriever u vc chunkconfig encryptor basek dest basep enc encc
 	firstavail (Just e) _ [] = throwM e
 	firstavail pe currsize ([]:ls) = firstavail pe currsize ls
 	firstavail _ currsize ((k:ks):ls)
-		| k == basek = do
-			iv <- startVerifyKeyContentIncrementally vc basek
-			getunchunked iv
-				`catchNonAsync` (\e -> firstavail (Just e) currsize ls)
+		| k == basek = getunchunked
+			`catchNonAsync` (\e -> firstavail (Just e) currsize ls)
 		| otherwise = do
 			let offset = resumeOffset currsize k
 			let p = maybe basep
 				(offsetMeterUpdate basep . toBytesProcessed)
 				offset
 			v <- tryNonAsync $
-				retriever (encryptor k) p $ \content ->
+				retriever (encryptor k) p Nothing $ \content ->
 					bracket (maybe opennew openresume offset) (liftIO . hClose . fst) $ \(h, iv) -> do
-						iv' <- retrieved iv (Just h) p content
+						retrieved iv (Just h) p content
 						let sz = toBytesProcessed $
 							fromMaybe 0 $ fromKey keyChunkSize k
-						getrest p h iv' sz sz ks
+						getrest p h iv sz sz ks
 			case v of
 				Left e
 					| null ls -> throwM e
@@ -313,12 +310,21 @@ retrieveChunks retriever u vc chunkconfig encryptor basek dest basep enc encc
 	getrest p h iv sz bytesprocessed (k:ks) = do
 		let p' = offsetMeterUpdate p bytesprocessed
 		liftIO $ p' zeroBytesProcessed
-		iv' <- retriever (encryptor k) p' $ 
+		retriever (encryptor k) p' Nothing $ 
 			retrieved iv (Just h) p'
-		getrest p h iv' sz (addBytesProcessed bytesprocessed sz) ks
+		getrest p h iv sz (addBytesProcessed bytesprocessed sz) ks
 
-	getunchunked iv = retriever (encryptor basek) basep $
-		retrieved iv Nothing basep
+	getunchunked = do
+		iv <- startVerifyKeyContentIncrementally vc basek
+		case enc of
+			Just _ -> retriever (encryptor basek) basep Nothing $
+				retrieved iv Nothing basep
+			-- Not chunked and not encrypted, so ask the
+			-- retriever to incrementally verify when it
+			-- retrieves to a file.
+			Nothing -> retriever (encryptor basek) basep iv $
+				retrieved iv Nothing basep
+		return iv
 
 	opennew = do
 		iv <- startVerifyKeyContentIncrementally vc basek
@@ -365,13 +371,11 @@ retrieveChunks retriever u vc chunkconfig encryptor basek dest basep enc encc
  - will be provided, and instead the content will be written to the
  - dest file.
  -
+ - The IncrementalVerifier is updated as the file content is read.
+ -
  - Note that when neither chunking nor encryption is used, and the remote
  - provides FileContent, that file only needs to be renamed
  - into place. (And it may even already be in the right place..)
- -
- - The IncrementalVerifier is updated as the file content is read.
- - If it was not able to be updated, due to the file not needing to be read,
- - Nothing will be returned.
  -}
 writeRetrievedContent
 	:: LensGpgEncParams encc
@@ -382,32 +386,25 @@ writeRetrievedContent
 	-> Maybe MeterUpdate
 	-> ContentSource
 	-> Maybe IncrementalVerifier
-	-> Annex (Maybe IncrementalVerifier)
+	-> Annex ()
 writeRetrievedContent dest enc encc mh mp content miv = case (enc, mh, content) of
 	(Nothing, Nothing, FileContent f)
-		| f == dest -> return Nothing
-		| otherwise -> do
-			liftIO $ moveFile f dest
-			return Nothing
+		| f == dest -> noop
+		| otherwise -> liftIO $ moveFile f dest
 	(Just (cipher, _), _, ByteContent b) -> do
 		cmd <- gpgCmd <$> Annex.getGitConfig
 		decrypt cmd encc cipher (feedBytes b) $
 			readBytes write
-		return miv
 	(Just (cipher, _), _, FileContent f) -> do
 		cmd <- gpgCmd <$> Annex.getGitConfig
 		withBytes content $ \b ->
 			decrypt cmd encc cipher (feedBytes b) $
 				readBytes write
 		liftIO $ removeWhenExistsWith R.removeLink (toRawFilePath f)
-		return miv
 	(Nothing, _, FileContent f) -> do
 		withBytes content write
 		liftIO $ removeWhenExistsWith R.removeLink (toRawFilePath f)
-		return miv
-	(Nothing, _, ByteContent b) -> do
-		write b
-		return miv
+	(Nothing, _, ByteContent b) -> write b
   where
 	write b = case mh of
 		Just h -> liftIO $ write' b h
diff --git a/Remote/Helper/Special.hs b/Remote/Helper/Special.hs
index e5d991b25f..37ea42caf4 100644
--- a/Remote/Helper/Special.hs
+++ b/Remote/Helper/Special.hs
@@ -1,6 +1,6 @@
 {- helpers for special remotes
  -
- - Copyright 2011-2020 Joey Hess <id@joeyh.name>
+ - Copyright 2011-2021 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -39,6 +39,7 @@ import Annex.Common
 import Annex.SpecialRemote.Config
 import Types.StoreRetrieve
 import Types.Remote
+import Annex.Verify
 import Annex.UUID
 import Config
 import Config.Cost
@@ -54,6 +55,8 @@ import Git.Types
 import qualified Data.ByteString as S
 import qualified Data.ByteString.Lazy as L
 import qualified Data.Map as M
+import Control.Concurrent.STM
+import Control.Concurrent.Async
 
 {- Special remotes don't have a configured url, so Git.Repo does not
  - automatically generate remotes for them. This looks for a different
@@ -101,19 +104,33 @@ fileStorer a k (ByteContent b) m = withTmp k $ \f -> do
 byteStorer :: (Key -> L.ByteString -> MeterUpdate -> Annex ()) -> Storer
 byteStorer a k c m = withBytes c $ \b -> a k b m
 
--- A Retriever that writes the content of a Key to a provided file.
--- It is responsible for updating the progress meter as it retrieves data.
-fileRetriever :: (FilePath -> Key -> MeterUpdate -> Annex ()) -> Retriever
-fileRetriever a k m callback = do
-	f <- prepTmp k
-	a (fromRawFilePath f) k m
-	pruneTmpWorkDirBefore f (callback . FileContent . fromRawFilePath)
-
 -- A Retriever that generates a lazy ByteString containing the Key's
 -- content, and passes it to a callback action which will fully consume it
 -- before returning.
-byteRetriever :: (Key -> (L.ByteString -> Annex a) -> Annex a) -> Key -> MeterUpdate -> (ContentSource -> Annex a) -> Annex a
-byteRetriever a k _m callback = a k (callback . ByteContent)
+byteRetriever :: (Key -> (L.ByteString -> Annex a) -> Annex a) -> Key -> MeterUpdate -> Maybe IncrementalVerifier -> (ContentSource -> Annex a) -> Annex a
+byteRetriever a k _m _miv callback = a k (callback . ByteContent)
+
+-- A Retriever that writes the content of a Key to a provided file.
+-- The action is responsible for updating the progress meter as it 
+-- retrieves data. The incremental verifier is updated in the background as
+-- the action writes to the file.
+fileRetriever :: (FilePath -> Key -> MeterUpdate -> Annex ()) -> Retriever
+fileRetriever a k m miv callback = do
+	f <- prepTmp k
+	let retrieve = a (fromRawFilePath f) k m
+	case miv of
+		Nothing -> retrieve
+		Just iv -> do
+			finished <- liftIO newEmptyTMVarIO
+			t <- liftIO $ async $ tailVerify iv f finished
+			retrieve
+			liftIO $ atomically $ putTMVar finished ()
+			liftIO (wait t) >>= \case
+				Nothing -> noop
+				Just deferredverify -> do
+					showAction (descVerify iv)
+					liftIO deferredverify
+	pruneTmpWorkDirBefore f (callback . FileContent . fromRawFilePath)
 
 {- The base Remote that is provided to specialRemote needs to have
  - storeKey, retrieveKeyFile, removeKey, and checkPresent methods,
diff --git a/Types/Backend.hs b/Types/Backend.hs
index 3d91fd5679..b8b9e71df9 100644
--- a/Types/Backend.hs
+++ b/Types/Backend.hs
@@ -52,4 +52,6 @@ data IncrementalVerifier = IncrementalVerifier
 	-- if the hash verified.
 	, failIncremental :: IO ()
 	-- ^ Call if the incremental verification needs to fail.
+	, descVerify :: String
+	-- ^ A description of what is done to verify the content.
 	}
diff --git a/Types/StoreRetrieve.hs b/Types/StoreRetrieve.hs
index 14453a3d82..8c0f61d930 100644
--- a/Types/StoreRetrieve.hs
+++ b/Types/StoreRetrieve.hs
@@ -1,6 +1,6 @@
 {- Types for Storer and Retriever actions for remotes.
  -
- - Copyright 2014 Joey Hess <id@joeyh.name>
+ - Copyright 2014-2021 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -11,6 +11,7 @@ module Types.StoreRetrieve where
 
 import Annex.Common
 import Utility.Metered
+import Types.Backend (IncrementalVerifier)
 
 import qualified Data.ByteString.Lazy as L
 
@@ -29,8 +30,17 @@ type Storer = Key -> ContentSource -> MeterUpdate -> Annex ()
 
 -- Action that retrieves a Key's content from a remote, passing it to a
 -- callback, which will fully consume the content before returning.
+--
 -- Throws exception if key is not present, or remote is not accessible.
-type Retriever = forall a. Key -> MeterUpdate -> (ContentSource -> Annex a) -> Annex a
+--
+-- When it retrieves FileContent, it is responsible for updating the
+-- MeterUpdate. And when the IncrementalVerifier is passed to it,
+-- and it retrieves FileContent, it should feed the content to the
+-- verifier before running the callback. 
+-- This should not be done when it retrieves ByteContent.
+type Retriever = forall a.
+	Key -> MeterUpdate -> Maybe IncrementalVerifier
+		-> (ContentSource -> Annex a) -> Annex a
 
 -- Action that removes a Key's content from a remote.
 -- Succeeds if key is already not present.