what happens to pool if ZIL dies on ZFS v14

[Jeremy Chadwick]

On Fri, Sep 17, 2010 at 09:21:54AM -0700, Freddie Cash wrote:
> On Fri, Sep 17, 2010 at 9:18 AM, Jeremy Chadwick
> <freebsd at jdc.parodius.com> wrote:
> > On Fri, Sep 17, 2010 at 09:17:11AM -0700, Freddie Cash wrote:
> >> On Fri, Sep 17, 2010 at 8:35 AM, Gil Vidals <gvidals at gmail.com> wrote:
> >> > Bryan thank you for the detailed answer.
> >> >
> >> > Assuming the ZIL SSD died, what steps would I follow to recover the pool? (i
> >> > hope it is recoverable).
> >>
> >> If you are running ZFSv1 through ZFSv18 and your log device dies, your
> >> pool is dead, gone, unrecoverable, no secret prize, no continues, do
> >> not pass go, etc, etc, etc.
> >>
> >> If you are running ZFSv19 or newer and your log device dies, you can
> >> remove the dead device and carry on.  You will lose any data that was
> >> in the ZIL, but the pool will be intact.
> >
> > Given the severity of this predicament, then why is it people are
> > disabling the ZIL (via vfs.zfs.zil_disable=1) ?
> 
> I'm not sure what you mean by that.
> 
> This (dead ZIL == dead pool) only applies to separate log (slog) devices.

I was under the impression ZFS still managed to utilise the ZIL when a
pool didn't have any "log" devices associated with it (possibly some
sort of statically-allocated amount of RAM?)

You can search the FreeBSD lists for people continually advocating
vfs.zfs.zil_disable=1.  There's even a couple blog posts from engineers
talking about how the only way to get their filers to behave decently
was to disable the ZIL[1][2][3].  In most (every?) cases I've seen where
someone advocates disabling the ZIL, pool details aren't provided, which
leads me to believe their pools have no "log" devices.

Here's a better way to phrase my question: does vfs.zfs.zil_disable=1 do
anything if there aren't any "log" devices in use (in any pool)?


[1]: http://jmlittle.blogspot.com/2010/03/zfs-log-devices-review-of-ddrdrive-x1.html
[2]: http://blogs.sun.com/erickustarz/entry/zil_disable
[3]: http://weblog.etherized.com/posts/130

-- 
| Jeremy Chadwick                                   jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |