On 2010-03-12 15:39, Craig White wrote: > On Fri, 2010-03-12 at 07:06 +0000, Jefferson Ogata wrote: >> On 2010-03-12 04:26, Craig White wrote: >>> On Fri, 2010-03-12 at 02:23 +0000, Jefferson Ogata wrote: >>>> On 2010-03-11 22:23, Matthew Geier wrote: >>>>> I've had a disk fail in such a way on a SCSI array that all disks on >>>>> that SCSI bus became unavailable simultaneously. When half the disks >>>>> dropped of the array at the same time, it gave up and corrupted the RAID >>>>> 5 meta data so that even after removing the offending drive, the array >>>>> didn't recover. >>>> I also should point out (in case it isn't obvious), that that sort of >>>> failure would take out the typical RAID 10 as well. >>> ---- >>> ignoring that a 2nd failed disk on RAID 5 is always fatal and only 50% >>> fatal on RAID 10, I suppose that would be true. >> The poster wrote that all of the disks on a bus failed, not just a >> second one. Depending on the RAID structure, this could take out a RAID >> 10 100% of the time. > ---- > actually, this is what he wrote... > > "When half the disks dropped of the array at the same time, it gave up > and corrupted the RAID 5 meta data so that even after removing the > offending drive, the array didn't recover." > > Half != all
Read it again: "I've had a disk fail in such a way on a SCSI array that all disks on that SCSI bus became unavailable simultaneously." Unless you have a disk on a separate bus for every mirror in the RAID 10, this will kill your RAID 10 100% of the time. While that configuration is more bulletproof, it also may not perform as well on a saturated RAID 10 since every write has to be queued to two separate buses instead of one. The original poster's failure was a recoverable one, anyway. He just didn't know the technique for recovery. > I had a 5 disk RAID 5 array fail the wrong disk and thus had 2 drives go > offline and had a catastophic failure and thus had to re-install and > recover from backup once (PERC 3/di & SCSI disks). Not something I wish > to do again. PERC 5 and PERC 6 are worlds different from the PERC 3/di. > I don't think I understand your 'odds' model. I interpret the first > example as RAID 50 having 5 times more likelihood of loss than RAID 10 > and I presume that isn't what you were after Yes, it is 5 times higher. But it is not 100%; it's actually less than 50%. And the probability for RAID 10 is not 50% as you said it was. I was just correcting your analysis. I'm still not sure what RAID structure you had in mind where a second failure on a RAID 10 has a 50% probability of loss. > ---- >> In the alternative fair comparison, RAID 5 vs. RAID 1, the second >> failure kills both RAIDs 100% of the time. > ---- > actually, I didn't raise the RAID 5 vs RAID 10 comparison, I only > amplified with my experiences You wrote: "ignoring that a 2nd failed disk on RAID 5 is always fatal and only 50% fatal on RAID 10, I suppose that would be true." That was you comparing RAID 5 with RAID 10. > the last time I bought an MD-1000, Dell would only sell me the PERC-5e, > I don't know why. Currently you can buy an MD1000 with or without a PERC 6. (If I could recommend an enclosure from a different manufacturer at this point, I would, but I haven't evaluated any others since I started buying MD1000s some years ago.) -- Jefferson Ogata : Internetworker, Antibozo <[email protected]> http://www.antibozo.net/ogata/ _______________________________________________ Linux-PowerEdge mailing list [email protected] https://lists.us.dell.com/mailman/listinfo/linux-poweredge Please read the FAQ at http://lists.us.dell.com/faq
