sstouffer Posted January 14, 2012 Share Posted January 14, 2012 According to this site: http://snapraid.sourceforge.net/compare.html unRAID doesn't have any kind of protection against bitrot or silent errors compared to some of the other options out there, like ZFS. Is that true? Does the parity drive in any way detect and correct these errors, or is it not happening until a dual-parity solution happens? I ask these questions because I'm currently running WHS v1 that has been giving me a few problems lately and I'm evaluating my other options out there. Thanks! Shawn Quote Link to comment
WeeboTech Posted January 14, 2012 Share Posted January 14, 2012 The parity drive can be used to detect and repair problems in sectors, but i don't think it's nearly as encompassing as ZFS. Many users do monthly parity checks to insure the arrays and drives have good integrity. Some users do periodic md5sums to detect issues at the file level. I do know that upon a drive failure, all drives, plus parity are used to virtually present the failed drive and rebuild it upon new drive installation. I'm, not sure of the exact rules of how parity correction works when single errors occur. Perhaps someone else will post more detail on this particular subject. Quote Link to comment
bubbaQ Posted January 14, 2012 Share Posted January 14, 2012 If you want to do an md5 snapshot of each file on a particular drive: find /mnt/disk1 -type f -exec md5sum {} \;>> /disk1_files.md5 Do it once a month. It then isn't hard to use something like beyond compare to use that output file and compare it to an older output file from the same command and look for changed lines, ignoring new/deleted lines. Quote Link to comment
marcusone Posted January 14, 2012 Share Posted January 14, 2012 If you want to do an md5 snapshot of each file on a particular drive: find /mnt/disk1 -type f -exec md5sum {} \;>> /disk1_files.md5 Do it once a month. It then isn't hard to use something like beyond compare to use that output file and compare it to an older output file from the same command and look for changed lines, ignoring new/deleted lines. How long does that take (and space) on a full 2TB drive (I know, depends on # of files, say 4,200 files)? Quote Link to comment
bubbaQ Posted January 15, 2012 Share Posted January 15, 2012 Speed is dependent on the number of bytes used on the disk and the disk read speed, because you are reading every byte of every file. Size of the resulting file, a rough upper-estimate is 100 bytes per file assuming your FQFN's are less than 70 characters.... so not much. Quote Link to comment
abs0lut.zer0 Posted January 15, 2012 Share Posted January 15, 2012 If you want to do an md5 snapshot of each file on a particular drive: find /mnt/disk1 -type f -exec md5sum {} \;>> /disk1_files.md5 Do it once a month. It then isn't hard to use something like beyond compare to use that output file and compare it to an older output file from the same command and look for changed lines, ignoring new/deleted lines. i sort of understand what you are talking about here, is there any chance of a better example with more verbose explanations please.. or maybe a wiki entry? Quote Link to comment
WeeboTech Posted January 15, 2012 Share Posted January 15, 2012 Check out md5deep also http://md5deep.sourceforge.net/ Read the documentation about md5sum and md5deep. It's basically a checksum of your files. The prior example uses find to traverse your filesystem and run md5sum on each fuile. md5deep can do the traversal within the program I have md5deep compiled for unRAID here: http://code.google.com/p/unraid-weebotech/downloads/list Quote Link to comment
WeeboTech Posted January 15, 2012 Share Posted January 15, 2012 Check out this other thread on the subject matter: http://lime-technology.com/forum/index.php?topic=13033.msg123555#msg123555 Quote Link to comment
dgaschk Posted January 15, 2012 Share Posted January 15, 2012 I installed md5deep using unMenu and it works flawlessly. Quote Link to comment
abs0lut.zer0 Posted January 15, 2012 Share Posted January 15, 2012 has any one experienced bitrot ? i know i have copied movies more than a year ago and not accessed them. Quote Link to comment
dgaschk Posted January 15, 2012 Share Posted January 15, 2012 I've never experienced it. Although, video files are not a good candidate for detecting bit rot. The errors will not be noticeable when viewing the video. Quote Link to comment
WeeboTech Posted January 15, 2012 Share Posted January 15, 2012 Only if the hard drive had pending_sectors. And that is pretty rare. Quote Link to comment
abs0lut.zer0 Posted January 16, 2012 Share Posted January 16, 2012 I've never experienced it. Although, video files are not a good candidate for detecting bit rot. The errors will not be noticeable when viewing the video. ahhh.. did not know that Quote Link to comment
dgaschk Posted January 16, 2012 Share Posted January 16, 2012 I've never experienced it. Although, video files are not a good candidate for detecting bit rot. The errors will not be noticeable when viewing the video. ahhh.. did not know that This assumes bit-rot is a single bit error. Effects will be greater for for multiple bit errors. If a b-frame (or slice) or p-frame has an error there's almost no chance of noticing. If an i-frame has an error it is unlikely you'll notice a transient effect but it will be fixed at the next i-frame, i.e, 1 to 15 frames later, depending on compression. Even in the worst case the error will effect the video for less than a second. Audio is even more robust to errors. Compression algorithms are designed to be robust in case of transmission (or storage) error. Quote Link to comment
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