Date: Wed, 19 Aug 2015 15:11:49 +0300 From: Daniel Kalchev <daniel@digsys.bg> To: javocado <javocado@gmail.com> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: Optimizing performance with SLOG/L2ARC Message-ID: <4BF27882-7BE1-480E-9903-434BDD202BB3@digsys.bg> In-Reply-To: <CAP1HOmTidC3%2BG4XfhvkQxieo%2BSYMq-JWiXF9Cs4FSW2VqkktWA@mail.gmail.com> References: <CAP1HOmTidC3%2BG4XfhvkQxieo%2BSYMq-JWiXF9Cs4FSW2VqkktWA@mail.gmail.com>
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> On 19.08.2015 =D0=B3., at 3:28, javocado <javocado@gmail.com> wrote: >=20 >=20 > 3. I know it's a good idea to mirror the SLOG (and I have). Do I = understand > correctly that I do not need to mirror the L2ARC since it's just a = read > cache, nothing to lose if the SSD goes down? >=20 There is a little known and grossly underestimated benefit of using = SLOG, even if it is not on SSD: less fragmentation in the pool. This is because, without SLOG ZFS will allocate the intent log records = from blocks in the pool. then free those blocks. These are all small = writes and leave behind a lot of holes. SLOG should be on it=E2=80=99s own drive anyway, normally, it=E2=80=99s = write-only and besides latency, a normal HDD should do as well. Of course, everything needs to be tested against the expected workload. Daniel
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