Date: Fri, 3 Oct 2014 15:34:34 +0100 From: Gary Palmer <gjp@in-addr.com> To: Warren Block <wblock@wonkity.com> Cc: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: Mirrored SSDs for ZIL/SLOG - safety, flushing, capacitors Message-ID: <20141003143434.GB41347@in-addr.com> In-Reply-To: <alpine.BSF.2.11.1410030547070.32407@wonkity.com> References: <CAP1HOmRYy8cX9k7rs4UEzx41Og4phX5U_2OpiUCKBDSRdMf_bQ@mail.gmail.com> <alpine.BSF.2.11.1410030547070.32407@wonkity.com>
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On Fri, Oct 03, 2014 at 05:59:48AM -0600, Warren Block wrote: > On Thu, 2 Oct 2014, javocado wrote: > > > I'm setting up a SLOG to improve performance on my ZFS-based fileserver. I > > plan to use 2 mirrored SSD's to create the log device. Before I continue, > > I have some specific questions how to approach which hardware to use. > > > > Primarily, I'm concerned with what damage/corruption may occur when there's > > a power loss. > > Do you have a good UPS? > > > 2. should I only use SSDs with capacitors? does anyone recommend any? I'm > > seeing good things about the Intel s3500 > > I think the Crucial M550 SSDs have additional backup capacitors also. > However, I'm still skeptical about the value of a small SSD power backup > versus a true UPS for the entire system. The point of the supercap is all SSDs (even the ones without proper power protection) have a small amount of DRAM which they use for write optimisation. The cap is just there to let the SSD dump the DRAM to flash if the power dies. Even with a good UPS you should still get SSDs with power protection in case of PSU failures or people knocking out power cords or something. Regards, Gary
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