Date: Fri, 21 Jan 2005 11:09:01 -0800 (PST) From: Don Lewis <truckman@FreeBSD.org> To: ertr1013@student.uu.se Cc: markir@paradise.net.nz Subject: Re: Disabling write-behind on IDE drives, and SMART Message-ID: <200501211909.j0LJ91MC052960@gw.catspoiler.org> In-Reply-To: <20050121164928.GA50279@falcon.midgard.homeip.net>
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On 21 Jan, Erik Trulsson wrote: > On Fri, Jan 21, 2005 at 08:31:06AM -0800, Kevin Oberman wrote: >> For servers that lack solid backup power (not a 10 minute >> UPS), I would probably turn it off. But for most systems it is probably >> worth the risks. > > A 10 minute UPS should be plenty for that purpose. All that is needed > to protect against the risks of write-caching is for the server to be > able to make an orderly shutdown, which should not take more than a > couple of minutes. (If you need constant uptime, you need better power > backup, but that is a different issue.) I guess that you haven't had as many UPS failures as I have had. The usual problem is sudden battery and unexpected battery death which brings the UPS runtime close to zero. The UPSes definitely help with the short hits to the power, but for anything important I pay the outrageously high premium for SCSI disks and turn off write caching. At least SCSI has working tagged command queuing that when used with softupdates avoids the performance hit caused by turning off write caching, at least for most workloads.
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