From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Nigel Roles" To: <9fans@cse.psu.edu> Subject: RE: [9fans] plan 9 ports to unix (including libdraw) Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit In-Reply-To: Date: Tue, 21 Oct 2003 07:28:18 +0100 Topicbox-Message-UUID: 75b8951c-eacc-11e9-9e20-41e7f4b1d025 9fans-admin@cse.psu.edu wrote: >>> real data. Especially now that my Venti server is mirrored >>> across two different-model 200GB IDE drives. >> >> How about IDE problem which Niger wrote. > > That's why I'm mirroring across two different-model 200GB drives. > The theory is that they're not that likely to fail simultaneously. > If you believe that a drive will fail once a year (which I think is > high) then two drives independently failing together will happen once > every few centuries, which is low enough that I can worry about > other problems, like my apartment catching fire. > > Russ It's certainly true that simultaneous failures are unlikely, and you should check your fire extinguisher in your apartment, but I think Geoff made the point a while back that the probability of failure for every given day is not 1/365.25; it starts high, drops to near zero, and then climbs rapidly in the few months before the warranty runs out. This is the "bath tub reliability curve". Also, if I cannot get to my machine for a few weeks, this significantly widens the window for a simultaneous failure. I think a few centuries is optimistic. In my case I'm more interested in having someone else already worked out how to replace and rebuild a drive when it fails, hence a need for a reputable RAID BIOS. Mentioning no names, our experience with SCSI U320 drives (i.e. the des. res. drives of the moment) is that price is not a guide to reliability.