Tim schrieb: > I'm sure you're already aware, but if not, 22 drives in a raid-6 is > absolutely SUICIDE when using SATA disks. 12 disks is the upper end of > what you want even with raid-6. The odds of you losing data in a 22 > disk raid-6 is far too great to be worth it if you care about your > data. /rant
Let's do some calculations. Based on the specs of http://www.seagate.com/docs/pdf/datasheet/disc/ds_barracuda_es_2.pdf AFR = 0.73% BER = 1:10^15 22 disk RAID-6 with 1TB disks. - The probability of a disk failure is 16.06% p.a. (0.73% * 22) - let's assume one day array rebuild time (22 * 1TB / 300MB/s) - This means the probability for another disk error during rebuild on the hot spare is is 0.042% (0.73% * (1/365) * 21) - If a second disk fails there is a chance of 16% of an unrecoverable read error on the remaining 20 disks (8 * 20 * 10^12 / 10^15) So the probability for a data loss is: 16.06% * 0.042% * 16.0% = 0.001% p.a. (a little bit higher since I haven't calculated 3 or more failing disks). The calculations assume an independent failure probability of each disk and correct numbers for AFR and BER. In reality I found the AFR rates of the disk vendors way too optimistic, but the BER rate too pessimistic. If we calculate with AFR = 3% BER = same we end up with with a data loss probability of 0.018% p.a. Daniel _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
