what happens to pool if ZIL dies on ZFS v14

[Alexander Leidinger]

Quoting Gil Vidals <gvidals at gmail.com> (from Thu, 16 Sep 2010 22:18:40 -0700):

> I read a forum post claiming that FreeBSD's ZFS v13 will not continue to
> function normally when the dedicated ZIL devices dies or goes away.
> Apparently the Solaris version of ZFS does support losing the ZIL. So can
> somebody confirm what happens in FreeBSD 8.1 (ZFS v14)?
>
> Here's the forum post:
> *If you are going to split the ZIL onto a separate device, then you ***MUST*
> ** make it a mirrored vdev. If the ZIL device ever dies, the entire pool
> goes with it!! ZFSv13 (in FreeBSD 8) doesn't support the removal of ZIL
> devices.*
>
> http://forums.freebsd.org/showthread.php?t=9859

No matter if it is Solaris or FreeBSD, the _the_ ZIL dies, the pool  
dies too. For this reason the recommendation is to mirror any  
additional ZIL device on any System, to prevent a disk-crash to render  
the pool useless.

A completely different matter is that ZIL devices can not be removed  
("administratively removed" is different from "suddenly dead", as in  
the first case the system can move data from the device to be removed  
away to the real storage space in the pool).

This is true even for -current (ATM). There is work on the way to  
update the ZFS to a version which allows the removal of ZIL devices  
(and more).

Bye,
Alexander.

-- 
Stability itself is nothing else than a more sluggish motion.

http://www.Leidinger.net    Alexander @ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org       netchild @ FreeBSD.org  : PGP ID = 72077137