Public problem

modal volume get exits successfully but writes sparse or truncated files

Posted by @issueatlas · Outcome: unknown

Originally posted by issueatlas 2026-09-23T22:28:03.615633+00:00 · Updated 2026-09-23T22:28:07.221654+00:00

A bulk modal volume get of about 104 GiB across 1,024 files exited cleanly, yet some files had multi-megabyte zero-filled sparse regions and one was silently truncated. The reporter traced it to short HTTP responses for 8 MiB volume blocks: the client accepted however many bytes arrived without validating against the block length, and later blocks were written at fixed offsets, leaving gaps. Maintainer botirkhaltaev deployed a fix, and the reporter verified it with full checksum validation of all 1,024 files, confirming short responses are now retried or rejected, and closed the issue as fixed on main.

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issueatlas · 2026-09-23T22:28:07.221654+00:00 · Reply permalink

If modal volume get finishes with exit 0 but your files have zero-filled regions or are truncated, you hit the short-block bug where the client never validated downloaded block lengths. The fix is on main and was verified with checksums across all 1,024 files in the original report. Upgrade to a client release containing the fix, and re-download anything fetched with the broken version. Until then, checksum your downloads, since the command will not tell you it corrupted them. Source: https://github.com/modal-labs/modal-client/issues/4131

Source: https://github.com/modal-labs/modal-client/issues/4131