Date: Fri, 15 Feb 2013 10:10:09 +0100 From: Daniel Kalchev <daniel@digsys.bg> To: grarpamp <grarpamp@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: Crazy ZFS ZIL options: md(4) umass(4) Message-ID: <43BC680B-4FC6-4CDB-A590-12ACC78959B7@digsys.bg> In-Reply-To: <CAD2Ti2_9i3rj5763UCjzxRw_7%2BqDky1MNRJzdvOZnmdYpLUfYQ@mail.gmail.com> References: <CAD2Ti2_9i3rj5763UCjzxRw_7%2BqDky1MNRJzdvOZnmdYpLUfYQ@mail.gmail.com>
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In short, don't. ZIL is not a cache. ZIL is there for you to recover transactions in case = of a crash. It is your safety net. If you don't have low latency SSD, put it on separate spinning disk, but = by all means never on RAM and USB only as a last resort, because USB is = slow for most uses and it is also extremely unreliable. Use the RAM for ARC, it will provide more performance. Daniel On Feb 15, 2013, at 10:00 AM, grarpamp <grarpamp@gmail.com> wrote: > I have thousands of small files being written most under 8KiB, they > either end up being removed or combined in various ways to > produce a set of data that is stored long term. I also have > tens of 10-50MiB files similarly, but rarely. It's not fully clear > to me the benefits of a split ZIL. Some say a split ZIL will ward > off some fragmentation, which pushing over 80% I'm sure to see > otherwise. Plus a speed boost if on faster media. And maybe > even no need to commit some ZIL to disk as small files are > removed before ZFS decides to aggregate? >=20 > Anyway, use case aside, I can put 1GiB of ram as ZIL.Same for 32GiB = USB. > RAM is obviously fast and power fail prone. > USB is slow and power safe. > Either could be mirrored, 2xRAM, 2xUSB. >=20 > - If I lose power on RAM, will the disk still be consistent? > - What data integrity does ZIL have? None? ZFS dataset's sha256? > - Any production experiences with this crazy ideas? >=20 > Thx. > _______________________________________________ > freebsd-fs@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org"
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