> From: Bob Friesenhahn [mailto:bfrie...@simple.dallas.tx.us] > Sent: Friday, December 17, 2010 9:16 PM > > While I agree that smaller vdevs are more reliable, your statement > about the failure being more likely be in the same vdev if you have > only 2 vdev's to be a rather useless statement. The probability of > vdev failure does not have anything to do with the number of vdevs. > However, the probability of vdev failure increases tremendously if > there is only one vdev and there is a second disk failure.
I'm not sure you got what I meant. I'll rephrase and see if it's more clear: Correct, the number of vdev's doesn't affect the probability of a failure in a specific vdev, but the number of disks in a vdev does. Lanky said he was considering 2x7disk raidz, versus 3x5disk raidz. So when I said he's more likely to have a 2nd disk fail in the same vdev if he only has 2 vdev's ... That was meant to be taken in context, not as a generalization about pools in general. Consider a single disk. Let P be the probability of the disk failing, within 1 day. If you have 5 disks in a raidz vdev, and one fails, there are 4 remaining. If resilver will last 8 days, then the probability of a 2nd disk failing is 4*8*P = 32P If you have 7 disks in a raidz vdev, and one fails, there are 6 remaining. If a resilver will last 12 days, then the probability of a 2nd disk failing is 6*12*P = 72P _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
