diff --git a/lib/build.ml b/lib/build.ml
index e3929516..8e2414a7 100644
--- a/lib/build.ml
+++ b/lib/build.ml
@@ -191,7 +191,7 @@ module Make (Raw_store : S.STORE) (Sandbox : S.SANDBOX) (Fetch : S.FETCHER) = st
     end >>!= fun src_dir ->
     let src_manifest = sequence (List.map (Manifest.generate ~exclude ~src_dir) src) in
     match Result.bind src_manifest (to_copy_op ~dst) with
-    | Error _ as e -> Lwt.return e
+    | Error _ as e -> Lwt.return (e :> ('a, [> `Msg of string | `Failed of (S.id * string) | `Cancelled ]) result)
     | Ok op ->
       let details = {
         base;
@@ -200,7 +200,7 @@ module Make (Raw_store : S.STORE) (Sandbox : S.SANDBOX) (Fetch : S.FETCHER) = st
       } in
       (* Fmt.pr "COPY: %a@." Sexplib.Sexp.pp_hum (sexp_of_copy_details details); *)
       let id = Sha256.to_hex (Sha256.string (Sexplib.Sexp.to_string (sexp_of_copy_details details))) in
-      Store.build t.store ?switch ~base ~id ~log (fun ~cancelled ~log result_tmp ->
+      let res = Store.build t.store ?switch ~base ~id ~log (fun ~cancelled ~log result_tmp ->
           let argv = `Run ["tar"; "-xf"; "-"] in
           let config = Config.v
               ~cwd:"/"
@@ -231,7 +231,8 @@ module Make (Raw_store : S.STORE) (Sandbox : S.SANDBOX) (Fetch : S.FETCHER) = st
           proc >>= fun result ->
           send >>= fun () ->
           Lwt.return result
-        )
+        ) in
+      (res : (string, [`Cancelled | `Failed of (S.id * string)]) Lwt_result.t :> (string, [> `Cancelled | `Msg of string | `Failed of (S.id * string) ]) Lwt_result.t)
 
   let pp_op ~(context:Context.t) f op =
     Fmt.pf f "@[<v2>%s: %a@]" context.workdir Obuilder_spec.pp_op op
@@ -255,25 +256,30 @@ module Make (Raw_store : S.STORE) (Sandbox : S.SANDBOX) (Fetch : S.FETCHER) = st
       result >>= fun result ->
       mount_secret values secret >>| fun resolved_secret ->
       (resolved_secret :: result) ) (Ok []) secrets
-
+  
   let rec run_steps t ~(context:Context.t) ~base = function
     | [] -> Sandbox.finished () >>= fun () -> Lwt_result.return base
     | op :: ops ->
       context.log `Heading Fmt.(str "%a" (pp_op ~context) op);
-      let k = run_steps t ops in
+      let k : context:Context.t -> base:string -> ( string, [ `Cancelled | `Failed of string * string | `Msg of string ] ) Lwt_result.t = fun ~context ~base ->
+        (run_steps t ops ~context ~base :> ( string, [ `Cancelled | `Failed of string * string | `Msg of string ] ) Lwt_result.t) 
+      in
       match op with
       | `Comment _ -> k ~base ~context
       | `Workdir workdir -> k ~base ~context:(update_workdir ~context workdir)
       | `User user -> k ~base ~context:{context with user}
-      | `Run { shell = cmd; cache; network; secrets = mount_secrets; rom } ->
+      | `Run { shell = cmd; cache; network; secrets = mount_secrets; rom } -> (
         let result =
           let { Context.switch; workdir; user; env; shell; log; src_dir = _; scope = _; secrets } = context in
           resolve_secrets secrets mount_secrets |> Result.map @@ fun mount_secrets ->
           (switch, { base; workdir; user; env; cmd; shell; network; mount_secrets }, log)
         in
         Lwt.return result >>!= fun (switch, run_input, log) ->
-        run t ~switch ~log ~cache ~rom run_input >>!= fun base ->
-        k ~base ~context
+        run t ~switch ~log ~cache ~rom run_input >>= fun base ->
+        match base with
+        | Ok base -> k ~base ~context
+        | Error _ as e -> Lwt.return e
+      )
       | `Copy x ->
         copy t ~context ~base x >>!= fun base ->
         k ~base ~context
@@ -356,7 +362,10 @@ module Make (Raw_store : S.STORE) (Sandbox : S.SANDBOX) (Fetch : S.FETCHER) = st
 
   let build t context spec =
     let r = build t context spec in
-    (r : (string, [ `Cancelled | `Msg of string ]) Lwt_result.t :> (string, [> `Cancelled | `Msg of string ]) Lwt_result.t)
+    (r : ( string,
+  [ `Cancelled | `Failed of string * string | `Msg of string ]
+)
+Lwt_result.t :> (string, [> `Cancelled | `Msg of string | `Failed of (S.id * string) ]) Lwt_result.t)
 
   let delete ?log t id =
     Store.delete ?log t.store id
@@ -638,7 +647,7 @@ module Make_Docker (Raw_store : S.STORE) = struct
 
   let build t context spec =
     let r = build ~scope:[] t context spec in
-    (r : (string, [ `Cancelled | `Msg of string ]) Lwt_result.t :> (string, [> `Cancelled | `Msg of string ]) Lwt_result.t)
+    (r :>  (string, [> `Cancelled | `Msg of string | `Failed of (S.id * string) ]) Lwt_result.t)
 
   let delete ?log t id =
     Store.delete ?log t.store id
diff --git a/lib/db_store.ml b/lib/db_store.ml
index 9c879dc5..8f5affb7 100644
--- a/lib/db_store.ml
+++ b/lib/db_store.ml
@@ -8,7 +8,7 @@ module Make (Raw : S.STORE) = struct
     mutable users : int;
     set_cancelled : unit Lwt.u;         (* Resolve this to cancel (when [users = 0]). *)
     log : Build_log.t Lwt.t;
-    result : (([`Loaded | `Saved] * S.id), [`Cancelled | `Msg of string]) Lwt_result.t;
+    result : (([`Loaded | `Saved] * S.id), [`Cancelled | `Failed of (S.id * string)]) Lwt_result.t;
     base : string option;
   }
 
@@ -69,10 +69,13 @@ module Make (Raw : S.STORE) = struct
           Lwt.wakeup set_log log;
           fn ~cancelled ~log dir
         )
-      >>!= fun () ->
-      let now = Unix.(gmtime (gettimeofday () )) in
-      Dao.add t.dao ?parent:base ~id ~now;
-      Lwt_result.return (`Saved, id)
+      >>= function 
+      | Ok () ->
+        let now = Unix.(gmtime (gettimeofday () )) in
+        Dao.add t.dao ?parent:base ~id ~now;
+        Lwt_result.return (`Saved, id)
+      | Error `Cancelled -> Lwt.return (Error `Cancelled)
+      | Error (`Msg m) -> Lwt.return (Error (`Failed (id, m)))
 
   let log_ty client_log ~id = function
     | `Loaded -> client_log `Note (Fmt.str "---> using %S from cache" id)
@@ -120,21 +123,25 @@ module Make (Raw : S.STORE) = struct
              (fun () -> get_build t ~base ~id ~cancelled ~set_log fn)
              (fun r ->
                 t.in_progress <- Builds.remove id t.in_progress;
-                Lwt.wakeup_later set_result r;
-                finish_log ~set_log log
+                finish_log ~set_log log >|= fun () ->
+                Lwt.wakeup_later set_result r
              )
              (fun ex ->
                 Log.info (fun f -> f "Build %S error: %a" id Fmt.exn ex);
                 t.in_progress <- Builds.remove id t.in_progress;
-                Lwt.wakeup_later_exn set_result ex;
-                finish_log ~set_log log
+                finish_log ~set_log log >|= fun () ->
+                Lwt.wakeup_later_exn set_result ex
              )
         );
       tail_log >>!= fun () ->
       result >>!= fun (ty, r) ->
       log_ty client_log ~id ty;
       Lwt_result.return r
-
+  
+  let build ?switch t ?base ~id ~log:client_log fn =
+    let res = build ?switch t ?base ~id ~log:client_log fn in
+    (res : (string, [ `Cancelled | `Failed of string * string ]) Lwt_result.t :> (string, [> `Cancelled | `Failed of string * string ]) Lwt_result.t)
+  
   let result t id = Raw.result t.raw id
   let count t = Dao.count t.dao
   let df t = Raw.df t.raw
diff --git a/lib/db_store.mli b/lib/db_store.mli
index 6610029c..6c0a70d4 100644
--- a/lib/db_store.mli
+++ b/lib/db_store.mli
@@ -7,7 +7,7 @@ module Make (Raw : S.STORE) : sig
     id:S.id ->
     log:S.logger ->
     (cancelled:unit Lwt.t -> log:Build_log.t -> string -> (unit, [`Cancelled | `Msg of string]) Lwt_result.t) ->
-    (S.id, [`Cancelled | `Msg of string]) Lwt_result.t
+    (S.id, [> `Cancelled | `Failed of (S.id * string)]) Lwt_result.t
   (** [build t ~id ~log fn] ensures that [id] is cached, using [fn ~cancelled ~log dir] to build it if not.
       If [cancelled] resolves, the build should be cancelled.
       If [id] is already in the process of being built, this just attaches to the existing build.
diff --git a/lib/rsync_store.ml b/lib/rsync_store.ml
index 6d94ea30..d72142f7 100644
--- a/lib/rsync_store.ml
+++ b/lib/rsync_store.ml
@@ -104,7 +104,7 @@ let build t ?base ~id fn =
     (fun r ->
       begin match r with
       | Ok () -> Rsync.rename_with_sharing ~mode:t.mode ~base ~src:result_tmp ~dst:result
-      | Error _ -> Rsync.delete result_tmp
+      | Error _ -> Rsync.rename_with_sharing ~mode:t.mode ~base ~src:result_tmp ~dst:result
       end >>= fun () ->
       Lwt.return r
     )
diff --git a/lib/s.ml b/lib/s.ml
index 4ce3ceab..97a6029c 100644
--- a/lib/s.ml
+++ b/lib/s.ml
@@ -109,7 +109,7 @@ module type BUILDER = sig
     t ->
     context ->
     Obuilder_spec.t ->
-    (id, [> `Cancelled | `Msg of string]) Lwt_result.t
+    (id, [> `Cancelled | `Msg of string | `Failed of (id * string)]) Lwt_result.t
 
   val shell :
     t ->
diff --git a/lib/zfs_store.ml b/lib/zfs_store.ml
index 974139f3..694c41ab 100644
--- a/lib/zfs_store.ml
+++ b/lib/zfs_store.ml
@@ -64,6 +64,7 @@ end = struct
 
   let state = "state"
   let result_group = "result"
+  let failed_group = "failed"
   let cache_group = "cache"
   let cache_tmp_group = "cache-tmp"
 
@@ -277,7 +278,8 @@ let build t ?base ~id fn =
         Lwt_result.return ()
       | Error _ as e ->
         Log.debug (fun f -> f "zfs: build %S failed" id);
-        Zfs.destroy t ds `And_snapshots >>= fun () ->
+        (* Don't delete build results that fail *)
+        (* Zfs.destroy t ds `And_snapshots >>= fun () -> *)
         Lwt.return e
     )
     (fun ex ->