`is_data_usage_cache_absent` matched `FileNotFound | VolumeNotFound`, but `SetDisks::get_object_reader` runs its failures through `to_object_err`, which rewrites those to `ObjectNotFound` and `BucketNotFound` before they reach the caller. The classifier therefore never matched in production: a cache object that simply does not exist was treated as a transient failure, retried five times with backoff, and then reported as an error instead of an empty cache. Admin server-info resolves one cache per erasure set, so that is roughly 1.5s of pointless backoff per set on any cluster whose scanner has not written a cache yet.
The same rewrite is why the pre-existing `FileNotFound | VolumeNotFound` arm in the old loop never fired either, which left the legacy-key fallback beside it unreachable — it only ever returned an empty cache through the catch-all break.
The classifier now covers the rewritten variants as well as the raw pair, the test store reports absence the way `to_object_err` does, and a new test pins which variants actually arrive.
Refs backlog#1828
Zhengchao An
bde6736213