Date: Mon, 11 Jan 2010 16:45:07 -0800 From: Freddie Cash <fjwcash@gmail.com> To: freebsd-fs@freebsd.org, FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org> Subject: Re: ZFS on top of GELI Message-ID: <b269bc571001111645n6b826dcfpa89f4388930db4cc@mail.gmail.com> In-Reply-To: <cf9b1ee01001111624h138633c0l5d021b9f9c2ee500@mail.gmail.com> References: <cf9b1ee01001100708m7851418cmbb77cc3580d0fab3@mail.gmail.com> <20100110161206.GA86684@plebeian.afflictions.org> <cf9b1ee01001101019o51e9a52fi6d02905914508706@mail.gmail.com> <20100110184612.GC86684@plebeian.afflictions.org> <cf9b1ee01001101128v5d636ab6p1fa3e5bcc713273d@mail.gmail.com> <82c4140e1001111529u7d7ac409h63dda4cc10b76522@mail.gmail.com> <cf9b1ee01001111624h138633c0l5d021b9f9c2ee500@mail.gmail.com>
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On Mon, Jan 11, 2010 at 4:24 PM, Dan Naumov <dan.naumov@gmail.com> wrote: > On Tue, Jan 12, 2010 at 1:29 AM, K. Macy <kmacy@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@gmail.com
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