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I sometimes find bit-rot in some of my files. This is rare, but does happen. It annoys me that this is a) undetected for long periods of time and b) not fixable (except from backups), even with the standard mirrored RAID.

I'm now looking for a solution to this issue. In particular, I'm thinking of a three-way mirrored RAID, so that whenever the bit rot is caused by a drive, it's possible to know which drive and to replicate the data from the other drives. Additionally, I'd have a scheduled task running every week or so to read everything off all drives and make sure it's still in sync.

The Windows 7 software RAID doesn't support having more than 2 drives in a mirrored set up. What other options are there to do this?

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ZFS is designed exactly to avoid this problem. –  sblair Sep 11 '11 at 14:19
    
@sblair yeah... shame it isn't supported on Windows. –  romkyns Sep 11 '11 at 15:14
    
I know, but if data integrity is the most important factor, then ZFS is the right tool for the job. Is this for the Windows boot drive? –  sblair Sep 11 '11 at 18:10
    
@sblair I would have said so too, but now that you mention it, the most important factor is to stay on Windows :) –  romkyns Sep 12 '11 at 9:04
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3 Answers 3

Check your cables. I just got a new pair of drives, and I was using an unopened (although old) set of SATA cables. Swapping out the cables immediately fixed my problems. I'm guess it's either bad cables, bad drive, bad memory, overclocking too high, or something along those lines. You're searching for a solution to a problem you shouldn't have. However, if you still find you are having problems, and want RAID to solve your problems, You can set up RAID5 on 3 drives, which has parity features built in, and should be able to correct some errors.

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Just to clarify, RAID 5 does not protect against bit rot because it is impossible to tell whether an error occurred in the data block or in the parity block. RAID 6 with regular data scrubbing should work though. –  sblair Sep 11 '11 at 18:54
    
One particular failure that I did manage to pinpoint and fix in the end was an overheating chip on the motherboard. I ran a piece of software that would write 20 GB of random data every night, then read it back and report errors, and once a week it would find a flipped bit. RAM tests showed up nothing, cable twiddling didn't help. Turning up my fans made this go away once and for all. Now the corruptions seem to correlate with bluescreens and lockups, both of which are far too rare for me to debug sensibly... –  romkyns Sep 12 '11 at 9:08
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"I sometimes find bit-rot in some of my files" You are focusing on relieving a symptom, not the problem. You should not be having data loss unless there is a virus or the hardware is defective.

I have 30 year old floppies that are perfectly readable, your modern hard drive should not be losing data.

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This is a bit like saying "you don't need checksums or error correcting codes; instead make it so that your data is never corrupted in the first place". I can't fix the huge variety of causes of data corruption. I need something practical. –  romkyns Sep 11 '11 at 18:05
    
you said it happens "sometimes" that means it happens often enough to be noticeable. Something is wrong with your system. –  Keltari Sep 11 '11 at 18:28
    
It's rare. To be specific: roughly twice a year, I find a file with a 8192 byte chunk of data that turned to zeroes. Sometimes it's a random app that reverted to default settings; I always look for this symptom in its config files then. Other times it's a source file I was coding. The first time I have seen this was in early 2000s on Win2K. I have seen it with this frequency on almost every PC I've had since then (which would be about 5 desktops + 1 laptop). –  romkyns Sep 12 '11 at 9:14
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romkyns if you want to stay in a windows environment (I don't have an interest in learning Solaris myself) you can get most the features of ZFS with Windows Server 2012 + rFS + storage spaces. Have a look at this blog post...

http://blogs.msdn.com/b/b8/archive/2012/01/16/building-the-next-generation-file-system-for-windows-refs.aspx

I don't think rFS was included in an client versions of windows yet, and these features don't work with NTFS, so you would have to move your data off win7 and use server 2012.

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