From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of Sigbjorn Lie
What about mirroring? Do I need mirrored ZIL devices in case of a power
outage?
You don't need mirroring for the sake of *power outage* but you *do* need
mirroring for the sake of preventing data loss when one of the SSD devices
fails. There is some gray area here:
If you have zpool < 19, then you do not have "log device removal" which
means you lose your whole zpool in the event of a failed unmirrored log
device. (Techniques exist to recover, but it's not always easy.)
If you have zpool >= 19, then the danger is much smaller. If you have a
failed unmirrored log device, and the failure is detected, then the log
device is simply marked "failed" and the system slows down, and everything
is fine. But if you have an undetected failure, *and* an ungraceful reboot
(which is more likely than it seems) then you risk up to 30 sec of data that
was intended to be written, immediately before the crash.
None of that is a concern, if you have a mirrored log device.
Ah, I see! Thanks.
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