> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Matthew Angelo > > My question is, how do I determine which of the following zpool and > vdev configuration I should run to maximize space whilst mitigating > rebuild failure risk? > > 1. 2x RAIDZ(3+1) vdev > 2. 1x RAIDZ(7+1) vdev > 3. 1x RAIDZ2(6+2) vdev > > I just want to prove I shouldn't run a plain old RAID5 (RAIDZ) with 8x > 2TB disks.
(Corrected type-o, 6+2 for you). Sounds like you made up your mind already. Nothing wrong with that. You are apparently uncomfortable running with only 1 disk worth of redundancy. There is nothing fundamentally wrong with the raidz1 configuration, but the probability of failure is obviously higher. Question is how do you calculate the probability? Because if we're talking abou 5e-21 versus 3e-19 then you probably don't care about the difference... They're both essentially zero probability... Well... There's no good answer to that. With the cited probability of bit error rate, you're just representing the probability of a bit error. You're not representing the probability of a failed drive. And you're not representing the probability of a drive failure within a specified time window. What you really care about is the probability of two drives (or 3 drives) failing concurrently... In which case, you need to model the probability of any one drive failing within a specified time window. And even if you want to model that probability, in reality it's not linear. The probability of a drive failing between 1yr and 1yr+3hrs is smaller than the probability of the drive failing between 3yr and 3yr+3hrs. Because after 3yrs, the failure rate will be higher. So after 3 yrs, the probability of multiple simultaneous failures is higher. I recently saw some seagate data sheets which specified the annual disk failure rate to be 0.3%. Again, this is a linear model, representing a nonlinear reality. Suppose one disk fails... How many weeks does it take to get a replacement onsite under the 3yr limited mail-in warranty? But then again after 3 years, you're probably considering this your antique hardware, and all the stuff you care about is on a newer server. Etc. There's no good answer to your question. You are obviously uncomfortable with a single disk worth of redundancy. Go with your gut. Sleep well at night. It only costs you $100. You probably have a cell phone with no backups worth more than that in your pocket right now. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
