Date: Wed, 19 Aug 2015 11:02:44 -0500 From: "Schweiss, Chip" <chip@innovates.com> To: PK1048 <paul@pk1048.com> Cc: javocado <javocado@gmail.com>, FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: Optimizing performance with SLOG/L2ARC Message-ID: <CALeZrrRex43B6N7GkTtaP36v5q7mQF8U9V1bU2W1%2B2uh8fhhiQ@mail.gmail.com> In-Reply-To: <023F881D-CCC5-4FCA-B09D-EB92C3BFBC03@pk1048.com> References: <CAP1HOmTidC3%2BG4XfhvkQxieo%2BSYMq-JWiXF9Cs4FSW2VqkktWA@mail.gmail.com> <023F881D-CCC5-4FCA-B09D-EB92C3BFBC03@pk1048.com>
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On Wed, Aug 19, 2015 at 10:29 AM, PK1048 <paul@pk1048.com> wrote: > > Please note that, depending on your workload, an SSD may _not_ be any > faster than a HDD. I am in the process of rebuilding a file server that > exhibited poor NFS SYNC write performance. Yet it had a mirrored pair of > SSDs. Unfortunately, those SSDs had _worse_ write performance than an HDD > for small (4 KB) writes. Based on recommendations from the OpenZFS list I > have a pair of Intel 3710 SSDs coming in to try, they are supposed to hav= e > much better write performance (at all block sizes) and much better > reliability long term (10x full disk writes per day for 5 years). I=E2=80= =99ll know > more once they arrive and I can test with them. > Pure SSD pools still need a log device. ZFS doesn't play well with the ZIL on the pool with SSDs. Even an SSD of the same type as the pool devices as the log device will fix the latency problem and throughput problems. It seems counter-intuitive but a very real problem, there is a long thread about this on the Illumos ZFS list. If you don't believe it, turn off sync on your SSD pool and performance will skyrocket. -Chip
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