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I've considered getting a commercial RAID NAS, e.g. QNAP or Synology but hesitate because I want to be absolutely confident regarding disaster recovery. I'd prefer not to be at the mercy of the manufacturer.

Suppose I've been a fool and not remembered that RAID is not a backup. One day a disk in my RAID 5 or 6 array fails, the box itself breaks, and I can't buy the same box again. Are there open source tools that can reliably rebuild my data on a new drive/array?

This is why I want to avoid drobo, but would welcome suggestions on good manufacturers or principles to make disaster recovery simple. E.g. what if I had a 4 bay NAS and set up 2x RAID 1 mirrors which were presented as one drive. In my scenario above would I be able to just copy directly off the healthy drives once plugged into a computer?

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Yes raid 1 mirror is the safest, the drive(s) can be read on another PC by itself, at the worst you will have to use "import foreign drive" in disk management to get it mounted in windows explorer. – Moab Nov 30 '10 at 22:25
up vote 2 down vote accepted

If you are serious about the NAS (eg: in a corporate environment), you cannot skimp on quality and must go for one that offers a 3 or 5 year warranty and on-site support. At the high end this means something like an HP Storageworks unit or similar, but I have also been looking at a Thecus 8800 unit, from a UK supplier that is Thecus appointed and who offers extended 3 year and 5 year warranties plus next day on-site support. For the cost of a single HP unit (about £9K for what we want), we can get 2 Thecus units (actually more!) and keep one as a warm or cold spare if we really want - and we probably will.

There is also the DIY approach where you control all the parts - I was also considering Chenbro or RSA2E cases stuffed with WD RE4 disks, but will probably go with the Thecus.

Also, skip RAID 5 and do RAID 6 or 10 + keep backups.

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if you do a DIY setup make sure to simulate a failure soon after setup so you know what to expect and how to act without risking critical data in the process. – Xantec Nov 30 '10 at 20:44
@Xantex Very good point about simulating failure. Will do that. – Pengin Nov 30 '10 at 21:03

Short answer: unless the manufacturer of NAS devices uses an industry standard tool for doing the RAID (e.g. FreeNAS), you're at their mercy if something should fail. You might be lucky, but I'd go with looking at that as my deciding factor.

Disclaimer: I really like the look of QNAP and probably won't follow my own advice.

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I think QNAP uses linux raid with a slightly modified on-disk format; it should be possible to recompile a kernel that supports it, using the sources QNAP provide. – Tobu Nov 30 '10 at 21:36
I think you're right. – user3463 Nov 30 '10 at 21:45

I first must recommend on a basic level at just having a full backup, totally separate, not in the same NAS box. That will keep chance of mistake to a minimum and probably allow you to have whatever degree of off-site protection you want as well. If you have a solid backup, you don't have to worry about losing your primary NAS. You also don't have to figure out how to recover, rebuild or whatever a RAID without using the normal access method and device. The highest quality NAS, warranty, support still cannot compete with a real backup.

Now since we're supposing there is no backup... If a disaster does happen, do not let anyone (including manufacturer support) reinitialize anything or make any changes. Make clones immediately (of the drives you can), and then you can try recovery attempts from the clones. This also lets you keep open the option of using a data recovery company if things are really bad.

I also agree about not bothering with RAID 5. Since FreeNAS was mentioned, I'll add that if you are running ZFS, you will run into some additional issues trying to access data outside the original configuration than you would with a traditional RAID. A basic software Linux RAID would allow you to take out the working disks from a failed machine and put them into a working machine and be recognized fairly easily.

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