RAID-6 and write hole with write-intent bitmap

Mukund Sivaraman
2020-11-24T07:26:18Z

Hi all

I am trying to setup a MD RAID-6 array and use the ext4 filesystem in
ordered mode (default) on it. The data gets backed up periodically. I
want the array to be always available.

I prefer not using a write-journal if it is sufficient for my usage. I
want to use the write-intent bitmap only. AIUI the write-hole problem
occurs when there is a crash or abrupt power off *and* disk failures.

* After a crash or abrupt power off, the write-intent bitmap is used to
rewrite parity where necessary. If there is no disk failure during
this period, is the RAID-6 array guaranteed to recover without
corruption?

With RAID-6, will recovery with write-intent bitmap succeed with 1
disk failure during the recovery period without a write-journal? i.e.,
is there a possibility of write hole with 1 disk failure in a RAID-6
array?

* With RAID-6 with write-intent bitmap in use, ext4 in ordered mode, no
disk failures, and abrupt power loss, is there any chance of data loss
in files other than those being written to just before the power loss?

(Apologies if these are silly questions, but I request answers.)

Mukund