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I'm considering building a storage solution where I would create one large LVM volume out of two or more pairs of disks, each pair running in RAID1. As far as I understand, this would let me expand the volume with more RAID1 pairs later on, and would allow one disk in each pair to fail simultaneously without any data being lost. However, should both disks in one pair fail at the same time, the whole volume will be lost.

Is this a bad idea, as far as reliability is concerned? The main increase in risk that I can see is that in the unlikely event that both disks in one pair fail at the same time, all data is lost, including data stored on other disk pairs. Are there other, more subtle, risks?

  • go for multiple raid10, share between seperate controllers + hosts, eliminate SPOF. remember sudden power loss problems with caching etc. 2 disk failing same time happens not so often, however during restore of the raid the 2nd (old) disk often(still rarely but risk is higher than normal operation) fails too, having to restore from backup, yes i personally have experienced exactly that (Raid1 1 drive down, replace broken drive, restore raid : about 60 or so percent of completion, the older drive failed as well.) – Dennis Nolte Mar 31 '17 at 8:22
  • @DennisNolte - one way to reduce the likelyhood of losing a second disk during rebuild is to turn on background scrubbing (if your raid controller supports it). This slowly (over weeks) reads every block on every disk, with the idea being that read errors will show up earlier, rather than while you're rebuilding. – Michael Kohne Mar 31 '17 at 11:12
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No, total loss of all data due to one pair going south is your main risk here. Are they all connected to the same controller? Are they all the same size? If so, can you perhaps organize it as a RAID 6?

You're obviously willing to spend half your drives on redundancy, and RAID 6 is able to survive loss of ANY two disks. All else being equal, I think the RAID 6 performance will be worse, though, and of course I'm assuming you've got them all on one controller which can do this.

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