SSD recommendations for ZFS cache/log

[Steven Hartland]

----- Original Message ----- 
From: "Tom Evans" <tevans.uk at googlemail.com>
To: "FreeBSD FS" <freebsd-fs at 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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