I still found it highly suspect that 6 drives would have failed so I ran a subsystem report and sent it off to Promise's tech support. Thankfully, this RAID was the clients versioned backup so worse case we replace the drives and reclone from the working RAID. Being that this was setup as a RAID 5 this posed some potential data loss. I wanted to document our solution in an effort to save you some time if you encounter this issue.Īfter a rather serious Florida Summertime storm all the drives on an R6 were showing up offline. After some back and forth with Promise tech support and conducting our own research we found a rather simple solution. We recently ran into an issue with the drives in the R6 showing up as Dead/Offline. They have a very robust Promise RAID setup (2 x R4 and 1x R6) with over 30TBs of storage. Do the math, that difference could be huge.ġ2-disk RAID10 using 12x2TB = 12TB usable.We have a client that does quite a bit of production work. Guess some people missed that memo.Īs for usable capacity, RAID10 is N/2, RAID5 is N-1. Still don't believe me? Plenty of documentation on the subject from Dell, EMC, Oracle.I thought for sure the RAID5 vs RAID10 write penalty was common knowledge. On paper you can argue RAID10 can survive double disk failure, but since we cannot predict when or where a drive is going to fail it's entirely possible to lose both disks in a mirror and boom, data loss. RAID5 has a write penalty of 4: Read old data, read old parity, write new data, write new parity.Īlso, don't mistake RAID10's additional mirror(s) as being more safe. RAID10 has a write penalty of 2 One write to each mirror. Under heavy write operations that write penalty with a factor of 4 and all the overhead will become your bottleneck. RAID5's write penalty is essentially double what it is for RAID10, RAID5 not only has to calculate the parity, it has to write that parity to disk.along with writing the data itself to disk, but only after reading the old data and parity. Repeating what you said before won't make it true.
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