Date: Fri, 9 Nov 2012 00:22:46 -0000 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Tom Evans" <tevans.uk@googlemail.com>, "FreeBSD FS" <freebsd-fs@freebsd.org> Subject: Re: SSD recommendations for ZFS cache/log Message-ID: <A357CF265EA8460ABFF1DBF3D0CA2947@multiplay.co.uk> References: <CAFHbX1K-NPuAy5tW0N8=sJD=CU0Q1Pm3ZDkVkE%2BdjpCsD1U8_Q@mail.gmail.com>
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----- Original Message -----
From: "Tom Evans" <tevans.uk@googlemail.com>
To: "FreeBSD FS" <freebsd-fs@freebsd.org>
Sent: Thursday, November 08, 2012 9:07 PM
Subject: SSD recommendations for ZFS cache/log
> 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.
New Intel drive announced the other day sounds nice, very much focused
on constant timings instead of streaming / random benchmarks.
Regards
Steve
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