* tiering: stop a shared remote object being deleted while replicas still point at it
A remote-tiered volume's .dat content lives only in one cloud object that all
N replica .vif files point at. Deleting that object while destroying any one
replica, or before a downloaded replica is durable, bricks the survivors.
- volume.tier.move cleanup now deletes old replicas with keepRemoteData=true so
surviving replicas keep the shared object. Document why the alreadyPlaced
anchor needs no replica sync (same-object replicas are byte-identical).
- VolumeTierMoveDatFromRemote now fsyncs the downloaded .dat, fsyncs the
containing directory, trims the .vif (fsynced) and swaps to the local DiskFile
BEFORE deleting the remote object, on both the keep-remote and delete paths.
Only the final DeleteFile is gated by keep_remote_dat_file, so a keep-remote
download leaves the replica served from local disk rather than the shared
object, and a crash before delete merely leaks the object.
- volume.tier.download keeps the shared object for every replica except the
last, which deletes it.
- s3 and rclone download paths fsync the .dat before close.
* storage: swap the volume data backend under the data lock
The tier-download swap closed v.DataBackend and assigned the new local DiskFile
without holding dataFileAccessLock, racing concurrent reads/writes (use of a
closed file / nil deref). Add an exported Volume.SwapDataBackend that performs
the close-and-replace under the lock, and call it from the tier download.
* server: skip directory fsync on Windows in the tier download path
os.Open(dir).Sync() is unsupported on Windows and returns an error, which would
fail VolumeTierMoveDatFromRemote entirely there. Skip the directory fsync on
Windows, matching how the storage-side helper tolerates the unsupported case.
* shell: make multi-replica tier.download resilient to already-local replicas
If a multi-replica download is interrupted and retried, a replica made local
in the prior attempt returns "already on local disk", which aborted the whole
command and left the remaining remote replicas dangling. Treat that case as a
skip-and-continue so a retry completes the rest.
* server: assert downloaded .dat content, not just length, in the tier test
A length-only check passes even if the bytes are corrupted; compare the full
content of the local .dat against the original.
Chris Lu