Date: Wed, 11 May 2011 14:17:42 +0300 From: Daniel Kalchev <daniel@digsys.bg> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: freebsd-fs@freebsd.org Subject: Re: ZFS: How to enable cache and logs. Message-ID: <4DCA7056.20200@digsys.bg> In-Reply-To: <20110511105117.GA36571@icarus.home.lan> References: <4DCA5620.1030203@dannysplace.net> <20110511100655.GA35129@icarus.home.lan> <4DCA66CF.7070608@digsys.bg> <20110511105117.GA36571@icarus.home.lan>
next in thread | previous in thread | raw e-mail | index | archive | help
On 11.05.11 13:51, Jeremy Chadwick wrote: > > Furthermore, TRIM support doesn't exist with ZFS on FreeBSD, so folks > should also keep that in mind when putting an SSD into use in this > fashion. > By the way, what would be the use of TRIM for SLOG and L2ARC devices? I see absolutely no benefit from TRIM for the L2ARC, because it is written slowly (on purpose). Any current, or 1-2 generations back SSD would handle that write load without TRIM and without any performance degradation. Perhaps TRIM helps with the SLOG. But then, it is wise to use SLC SSD for the SLOG, for many reasons. The write regions on the SLC NAND should be smaller (my wild guess, current practice may differ) and the need for rewriting will be small. If you don't need to rewrite already written data, TRIM does not help. Also, as far as I understand, most "serious" SSDs (typical for SLC I guess) would have twice or more the advertised size and always write to fresh cells, scheduling an background erase of the 'overwritten' cell. Does Solaris have TRIM for ZFS? Where? How does it help? I can imagine TRIM for the data pool, that would be good fit for ZFS, but SSD-only pool.. are we already there? Daniel
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?4DCA7056.20200>