Erasure heal set write_quorum to the count of available target writers,
so every replacement disk had to succeed writing every block or the whole
object heal aborted. A single flapping replacement disk failing one block
made MultiWriter::write return Err, heal propagate Err, and the ops layer
delete the entire tmp staging dir — leaving the other healthy replacement
disks unhealed and blocking redundancy recovery indefinitely.
Set the heal write_quorum to 1, matching upstream MinIO's writeQuorum=1
for heal. MultiWriter already marks a failed writer as None, and the ops
layer (set_disk/ops/heal.rs) already drops the failed writer while
committing the survivors; the read-side quorum check and parity
cross-checks that guarantee reconstruction correctness are unchanged.
Add regression tests: one healthy-and-one-failing target still heals the
healthy targets and drops the failing one; all-targets-failing still
returns Err so nothing is falsely committed.
Fixes#947
Co-authored-by: heihutu <[email protected]>
