Date: Mon, 11 Jan 2010 23:00:09 -0500 From: jhell <jhell@DataIX.net> Cc: freebsd-fs@freebsd.org, FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org> Subject: Re: ZFS on top of GELI Message-ID: <alpine.BSF.2.00.1001112231170.45901@pragry.qngnvk.ybpny> In-Reply-To: <b269bc571001111645n6b826dcfpa89f4388930db4cc@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> <b269bc571001111645n6b826dcfpa89f4388930db4cc@mail.gmail.com>
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Mon, 11 Jan 2010 19:45, fjwcash@ wrote: > 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. > > What I have seen more often by users is taking the usage of slog/ZIL wrong. For instance dedicating a whole SSD or another HDD as the slog. Your slog/ZIL only has to be big enough to handle 10 seconds of synchronous writes before it flushes. A recommended ZIL from Sun Micro is 128MB but you may not even see that fully used for general purpose cases. I had is to dedicate a partition on the same disk that the pool is on and adding another ZIL vdev from another disk in the system. Results of this imply that if the off-disk ZIL dies for some stupid reason it falls back to the one that rests on the same disk as the pool and allows to replace the off-disk ZIL with something else. PS: Save your disk space and use 256MB thumb drives. you can easily get 16 of those at your local Walmart and have a priceless light show for a romantic dinner with the wife. :) - -- Mon Jan 11 22:31:17 2010 jhell -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (FreeBSD) iQEcBAEBAgAGBQJLS/PZAAoJEJBXh4mJ2FR+CTUH/RIqmRPE8SdKZYY7WIC/K9Yk HThaiYHs6a15ZY58q2nHG0x5J85TOBMN4yvC1rI1DGcjX9SXlyjxY+jJ0sdIAbHz N2+nT95X3SbNCPXtA3qo6uTplIiZnu9xgcAnFmjBh96Aq7qzcIvtFe2QMuxTp/lI Na8K4t7udDFQ9xIoyptk/PukKvV/EtzDx449w6VPxu0fkXK812uWWl+jFy3XchrW QfExuNIhVadcnxOB5/BQaAyd6daaI9tZNyARo43ww7bEKxaFP2Awre/IYfeuKZtm /n4TOdOoookyIIO0fMWDQ4WyLLsQD6eHug0B0Ef7LYcrUkPEYFJQVxujhx/cyhI= =cjuO -----END PGP SIGNATURE-----
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