Concern: ZFS Mirror issues (12.STABLE and firmware 19 .v. 20)

Andriy Gapon avg at
Wed Apr 10 13:45:50 UTC 2019

On 10/04/2019 04:09, Karl Denninger wrote:
> Specifically, I *explicitly* OFFLINE the disk in question, which is a
> controlled operation and *should* result in a cache flush out of the ZFS
> code into the drive before it is OFFLINE'd.
> This should result in the "last written" TXG that the remaining online
> members have, and the one in the offline member, being consistent.
> Then I "camcontrol standby" the involved drive, which forces a writeback
> cache flush and a spindown; in other words, re-ordered or not, the
> on-platter data *should* be consistent with what the system thinks
> happened before I yank the physical device.

This may not be enough for a specific [RAID] controller and a specific
configuration.  It should be enough for a dumb HBA.  But, for example, mrsas(9)
can simply ignore the synchronize cache command (meaning neither the on-board
cache is flushed nor the command is propagated to a disk).  So, if you use some
advanced controller it would make sense to use its own management tool to
offline a disk before pulling it.

I do not preclude a possibility of an issue in ZFS.  But it's not the only
possibility either.

Andriy Gapon

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