diff --git a/mirage/unikernel.ml b/mirage/unikernel.ml
index 51da59a..5bda300 100644
--- a/mirage/unikernel.ml
+++ b/mirage/unikernel.ml
@@ -154,6 +154,34 @@ module Make
         SM.empty opam_paths
   end
 
+  let active_downloads = ref SM.empty
+
+  let add_to_active url ts =
+    active_downloads := SM.add url (ts, 0, "unknown size") !active_downloads
+
+  let remove_active url =
+    active_downloads := SM.remove url !active_downloads
+
+  let active_length url written length =
+    match SM.find_opt url !active_downloads with
+    | None -> ()
+    | Some (ts, written', _) ->
+      active_downloads := SM.add url (ts, written + written', length)
+          !active_downloads
+
+  let active_add_bytes url written =
+    match SM.find_opt url !active_downloads with
+    | None -> ()
+    | Some (ts, written', l) ->
+      active_downloads := SM.add url (ts, written + written', l)
+          !active_downloads
+
+  let failed_downloads = ref SM.empty
+
+  let add_failed url ts reason =
+    remove_active url;
+    failed_downloads := SM.add url (ts, reason) !failed_downloads
+
   module Disk = struct
     type t = {
       mutable md5s : string SM.t ;
@@ -169,7 +197,6 @@ module Make
 
     let empty dev dev_md5s dev_sha512s = { md5s = SM.empty ; sha512s = SM.empty ; dev; dev_md5s; dev_sha512s }
 
-
     let marshal_sm (sm : string SM.t) =
       let version = char_of_int 1 in
       String.make 1 version ^ Marshal.to_string sm []
@@ -305,7 +332,7 @@ module Make
       in
       Mirage_kv.Key.(to_delete / hash_to_string hash / (encoded_csum ^ "." ^ rand))
 
-    let write_partial t (hash, csum) =
+    let write_partial t (hash, csum) url =
       (* XXX: we may be in trouble if different hash functions are used for the same archive *)
       let key = pending_key (hash, csum) in
       let ( >>>= ) = Lwt_result.bind in
@@ -324,8 +351,10 @@ module Make
             |> Lwt_result.map_error (fun e -> `Write_error e) >>>= fun () ->
             let len = String.length data in
             let offset = Optint.Int63.of_int len in
+            active_length url len (Int64.to_string size ^ " bytes");
             Lwt.return_ok (digests, `Fixed_body (size, offset))
           | `Unknown ->
+            active_add_bytes url (String.length data);
             Lwt.return_ok (digests, `Unknown data)
           end
         | `Fixed_body (size, offset) ->
@@ -333,8 +362,10 @@ module Make
           |> Lwt_result.map_error (fun e -> `Write_error e) >>>= fun () ->
           let len = String.length data in
           let offset = Optint.Int63.(add offset (of_int len)) in
+          active_add_bytes url len;
           Lwt.return_ok (digests, `Fixed_body (size, offset))
         | `Unknown body ->
+          active_add_bytes url (String.length data);
           Lwt.return_ok (digests, `Unknown (body ^ data))
 
     let check_csums_digests csums digests =
@@ -368,18 +399,29 @@ module Make
         | `Init -> assert false
         end >|= function
         | Ok () ->
+          remove_active url;
           t.md5s <- SM.add md5 sha256 t.md5s;
           t.sha512s <- SM.add sha512 sha256 t.sha512s
         | Error e ->
-          Logs.err (fun m -> m "Write failure for %s: %a" url KV.pp_write_error e)
+          Logs.err (fun m -> m "Write failure for %s: %a" url KV.pp_write_error e);
+          add_failed url (Ptime.v (Pclock.now_d_ps ()))
+            (Fmt.str "Write failure for %s: %a" url KV.pp_write_error e)
       else begin
-        (if sizes_match then
+        (if sizes_match then begin
+           add_failed url (Ptime.v (Pclock.now_d_ps ()))
+             (Fmt.str "Bad checksum %s:%s: computed %s expected %s" url
+                        (hash_to_string hash)
+                        (Ohex.encode (Archive_checksum.get digests hash))
+                        (Ohex.encode csum));
            Logs.err (fun m -> m "Bad checksum %s:%s: computed %s expected %s" url
                         (hash_to_string hash)
                         (Ohex.encode (Archive_checksum.get digests hash))
                         (Ohex.encode csum))
-         else match body with
+         end else match body with
            | `Fixed_body (reported, actual) ->
+             add_failed url (Ptime.v (Pclock.now_d_ps ()))
+               (Fmt.str "Size mismatch %s: received %a bytes expected %Lu bytes"
+                  url Optint.Int63.pp actual reported);
              Logs.err (fun m -> m "Size mismatch %s: received %a bytes expected %Lu bytes"
                           url Optint.Int63.pp actual reported)
            | `Unknown _ -> assert false
@@ -404,7 +446,6 @@ module Make
           Lwt.return_unit
       end
 
-
     (* on disk, we use a flat file system where the filename is the sha256 of the data *)
     let init ~verify_sha256 dev dev_md5s dev_sha512s =
       KV.list dev Mirage_kv.Key.empty >>= function
@@ -682,6 +723,37 @@ stamp: %S
             t.index <- index;
             Some changes)
 
+    let status disk =
+      (* report status:
+         - archive size (can we easily measure?) and number of "good" elements
+         - list of current downloads
+         - list of failed downloads
+      *)
+      let hashes = SM.cardinal disk.Disk.md5s in
+      let archive_stats = Printf.sprintf "%u validated archives on disk" hashes in
+      let active_downloads =
+        let header = "<h2>Active downloads</h2><ul>" in
+        let content =
+          SM.fold (fun url (ts, bytes_written, length_or_unknown) acc ->
+              ("<li>" ^ Ptime.to_rfc3339 ?tz_offset_s:None ts ^ ": " ^ url ^ " " ^ string_of_int bytes_written ^ " bytes written to disk, " ^ length_or_unknown ^ "</li>")
+              ^ acc)
+            !active_downloads ""
+        in
+        header ^ content ^ "</ul>"
+      and failed_downloads =
+        let header = "<h2>Failed downloads</h2><ul>" in
+        let content =
+          SM.fold (fun url (ts, reason) acc ->
+              ("<li>" ^ Ptime.to_rfc3339 ?tz_offset_s:None ts ^ ": " ^ url ^ " " ^ reason ^ "</li>")
+              ^ acc)
+            !failed_downloads ""
+        in
+        header ^ content ^ "</ul>"
+      in
+      "<html><head><title>Opam-mirror status page</title></head><body><h1>Opam mirror status></h1><div>"
+      ^ String.concat "</div><div>" [ archive_stats ; active_downloads ; failed_downloads ]
+        ^ "</div></body></html>"
+
     let not_modified request (modified, etag) =
       match Httpaf.Headers.get request.Httpaf.Request.headers "if-modified-since" with
       | Some ts -> String.equal ts modified
@@ -734,6 +806,16 @@ stamp: %S
         let headers = Httpaf.Headers.of_list headers in
         let resp = Httpaf.Response.create ~headers `OK in
         Httpaf.Reqd.respond_with_string reqd resp data
+      | [ ""; x ] when String.equal x "status" ->
+        let data = status store in
+        let mime_type = "text/html" in
+        let headers = [
+          "content-type", mime_type ;
+          "content-length", string_of_int (String.length data) ;
+        ] in
+        let headers = Httpaf.Headers.of_list headers in
+        let resp = Httpaf.Response.create ~headers `OK in
+        Httpaf.Reqd.respond_with_string reqd resp data
       | [ ""; "repo" ] ->
         if not_modified request (t.modified, t.commit_id) then
           let resp = Httpaf.Response.create `Not_modified in
@@ -843,18 +925,23 @@ stamp: %S
           if !idx mod 10 = 0 then Gc.full_major () ;
           Logs.info (fun m -> m "downloading %s" url);
           let quux, body_init = Archive_checksum.init_write csums in
-          Http_mirage_client.request http_client url (Disk.write_partial disk quux) body_init >>= function
+          add_to_active url (Ptime.v (Pclock.now_d_ps ()));
+          Http_mirage_client.request http_client url (Disk.write_partial disk quux url) body_init >>= function
           | Ok (resp, r) ->
             begin match r with
               | Error `Bad_response ->
                 Logs.warn (fun m -> m "%s: %a (reason %s)"
                               url H2.Status.pp_hum resp.status resp.reason);
+                add_failed url (Ptime.v (Pclock.now_d_ps ()))
+                  (Fmt.str "%a %s" H2.Status.pp_hum resp.status resp.reason);
                 Lwt.return_unit
               | Error `Write_error e ->
                 Logs.err (fun m -> m "%s: write error %a %a"
                               url
                               Mirage_kv.Key.pp (Disk.pending_key quux)
                               KV.pp_write_error e);
+                add_failed url (Ptime.v (Pclock.now_d_ps ()))
+                  (Fmt.str "write error: %a" KV.pp_write_error e);
                 Lwt.return_unit
               | Ok (digests, body) ->
                 Disk.finalize_write disk quux ~url body csums digests