[OpenIndiana-discuss] Recovering from power loss on USB ZFS pool?

[Jonathan Adams]

On 27 March 2014 18:28, Reginald Beardsley <pulaskite at yahoo.com> wrote:

> What's the correct way to recover from loss of power to a USB disk based
> pool?
>
> I cleverly unplugged the wrong wall wart from the power strip behind my
> monitor and dropped power to a USB disk that was being written to.  The
> system stayed up, but any attempt to restart or kill the write operation
> failed and attempts  to query the status of the pool hung.  I tried to
> restart the system, but that hung also and ultimately I forced the system
> down w/ the power switch.  It rebooted w/o any problems.
>
> The  SATA drive scrubs showed they were  OK.  The USB scrub is still
> running, but the pool seemed OK after the reboot.
>
> Surely there is a better way to recover from such things than just killing
> the power.  google didn't seem to have any suggestions so I thought I'd ask
> here.
>

from my experience with USB zfs systems, there is no better way :(

>From my experience, when a USB drive goes off on one (doesn't necessarily
even need powering off) it kills the whole ZFS until the point that you
have to reboot the machine, as long as you don't have too many USB devices
plugged in on a reboot it should recover and scrub happily.

We have had several machines with USB drives that caused us problems.

1) we have a machine with an irregularly used USB drive ... sometimes the
drive fails to talk to ZFS when it is waking up out of sleep mode ... the
only reason we can reboot that one is that it's a Solaris 10 with UFS root
filesystem
2) we had big Arrays > 8 disks plugged in over USB ... if we had plugged a
keyboard in during it's uptime, and forgot to unplug it the drives wouldn't
import, if we plug the keyboard in the front sockets of the machine the ZFS
hangs.

strangely enough we don't have any more free floating ZFS usb drives (6
T710's bought to house the USB arrays internally) except to perform
sneakernet operations.

on a positive note, taking an unreliable old USB ZFS pool off of a
misbehaving Solaris 10 box and plugging into an Ubuntu with ZFS allowed the
USB drive to work flawlessly for a long time thereafter ... Ubuntu ZFS
seems a lot more stable and reliable than the Solaris/Illumos equivalent.
If you have future trouble (and you haven't upgraded your ZFS on Illumos to
the latest greatest hipster version) you should be able to get your data
back.

Jon