Does anyone know what would happen if an external hard drive that was part of a set of spanned discs was powered off whilst the computer was running? Also what would happen if it was turned off before the computer booted and windows couldn't find it?

Would the whole virtual drive just disappear from my computer and re-appear again afterwards when all the discs are available or would it break it?

I'm using windows 7 ultimate.



I've had this happen (because of a SATA disconnect, not an external drive being powered off), and the spanned volume malfunctioned. After manually adding the separate disks again to the computer, I was able to get most of my data back (but not files that spanned the "break points"), and learned a valuable lesson:

Spanning volumes is dangerous. Don't use it unless it's running on top of some other redundancy (like RAID or a good backup), and I think it's a VERY bad idea to have spanned volumes that are external disks and can lose connection easily, at the kick of a power brick or pull of a USB cable.

  • What would happen if there was a power cut or I had to do a hard reset? Is the chance of data loss roughly the same as the chance with one drive (which I presume is relatively low) or is there a very high chance of loosing things? It's bound to get a bsod or completely lock up some time. Thanks. – Tom Jenkinson Jun 10 '12 at 21:12
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    Even in a normal set up you may lose data as in the write process as it may be in the disk's cache. In spanning (not striping) the risk of losing data is probably no greater during a power fail. However I must agree with Zac B, it is dangerous and doing it with external volumes is even worse especially as USB can also throw a fit and disconnect at times. If you want data to be safe and are doing it cheaply either use RAID1 and/or regular backups. Spanning, Striping and distributed RAID is risky especially with external drives, cheap drives or cheap controllers. – Paul Ridgway Jun 10 '12 at 22:33
  • With any sort of live parity (like RAID1), the risk of corruption in the event of a power loss is the same as if you had one disk: if a boot-critical file is in the process of being rewritten when you lose power, it's partially written on both RAID disks, same as it would be on just one disk. That's why half of any good disaster recovery plan is good backups that are taken offline and kept in case of corruption. – Zac B Jun 11 '12 at 18:08
  • Also, even for small desktop environments, a good UPS that will give you the 5 or 6 minutes you need to save all of your open files and shut down is a really great asset. You can get one cheaply, and in many cases can even interface the computer with it to initiate a soft shutdown in the event of a power loss. – Zac B Jun 11 '12 at 18:08

Spanned in the RAID sense? It would break the array, with potential loss of data.

  • this (the first option). I think it's similar to a raid. My external backup drive is getting full and I'm not sure whether to extend it onto another external drive. If everything on them both becomes unreadable if the power goes off then I'm thinking it's probably not the best idea. – Tom Jenkinson May 30 '12 at 14:56
  • Yeah, that's not a good idea; the best way is to partition your use of the backup disk somehow, perhaps by source folder. – pjc50 May 30 '12 at 14:58
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    Of course, with real RAID (where the "R" actually means "redundant") there should be no loss. With some versions you could just keep running. But what's called "RAID" anymore very often isn't. – Daniel R Hicks May 30 '12 at 15:10
  • @pjc50 what do you mean? I'm using windows backup and would like it to all run in one job. The problem is that I don't really want to allocate certain folders to backup to a certain drive as then I'm ending up wasting space. – Tom Jenkinson May 30 '12 at 15:33

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