ZFS on top of GELI

[Freddie Cash]

On Mon, Jan 11, 2010 at 4:24 PM, Dan Naumov <dan.naumov at gmail.com> wrote:

> On Tue, Jan 12, 2010 at 1:29 AM, K. Macy <kmacy at freebsd.org> wrote:
> >>>
> >>> If performance is an issue, you may want to consider carving off a
> partition
> >>> on that SSD, geli-fying it, and using it as a ZIL device.  You'll
> probably
> >>> see a marked performance improvement with such a setup.
> >>
> >> That is true, but using a single device for a dedicated ZIL is a huge
> >> no-no, considering it's an intent log, it's used to reconstruct the
> >> pool in case of a power failure for example, should such an event
> >> occur at the same time as a ZIL provider dies, you lose the entire
> >> pool because there is no way to recover it, so if ZIL gets put
> >> "elsewhere", that elsewhere really should be a mirror and sadly I
> >> don't see myself affording to use 2 SSDs for my setup :)
> >>
> >
> > This is  false. The ZIL is used for journalling synchronous writes. If
> > your ZIL is lost you will lose the data that was written to the ZIL,
> > but not yet written to the file system proper. Barring disk
> > corruption, the file system is always consistent.
> >
> > -Kip
>
> Ok, lets assume we have a dedicated ZIL on a single non-redundant
> disk. This disk dies. How do you remove the dedicated ZIL from the
> pool or replace it with a new one? Solaris ZFS documentation indicates
> that this is possible for dedicated L2ARC - you can remove a dedicated
> l2arc from a pool at any time you wish and should some IO fail on the
> l2arc, the system will gracefully continue to run, reverting said IO
> to be processed by the actual default built-in ZIL on the disks of the
> pool. However the capability to remove dedicated ZIL or gracefully
> handle the death of a non-redundant dedicated ZIL vdev does not
> currently exist in Solaris/OpenSolaris at all.
>
> That has been implemented in OpenSolaris, do a search for "slog removal".
 It's in a much newer zpool version than 13, though.

-- 
Freddie Cash
fjwcash at gmail.com