Date: Thu, 8 Nov 2012 21:07:24 +0000 From: Tom Evans <tevans.uk@googlemail.com> To: FreeBSD FS <freebsd-fs@freebsd.org> Subject: SSD recommendations for ZFS cache/log Message-ID: <CAFHbX1K-NPuAy5tW0N8=sJD=CU0Q1Pm3ZDkVkE%2BdjpCsD1U8_Q@mail.gmail.com>
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Hi all I'm upgrading my home ZFS setup, and want to speed things up a bit by adding some SSDs for cache/log. I was hoping some more experienced heads could offer some advice on what I've gleaned so far. I've read that the Sandforce based devices get their astonishing write speeds from compressible data, and that on random data, it is significantly worse, so comparing headline write speeds is not that useful. I've also read that MLC flash is significantly slower writing to the 2nd bit, and so the drive firmware will constantly be moving bits in the background from 1st bit to 2nd bit, in order to keep high write speeds, and so the firmware is specially important, which to my mind rules out devices using stock Sandforce firmware (everyone but Intel), and OCZ, who I've read too many horror stories about. This is a home setup, so SLC is out unfortunately. Is it still recommended to have a mirror for log device, now that pools can survive losing a log device unexpectedly? I was planning to get two 128GB drives, and slice them up 4/8/20/96 for UFS root, swap, log, cache respectively, but I could instead get a single larger and faster drive. The drives I am thinking of getting are either Intel 330, Intel 520, Crucial M4 RealSSD or Samsung 830, all in their 120/128GB variants. Any advice gratefully accepted. Cheers Tom
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