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| Help me Nancy Drew this computer mystery... https://gladerebooted.net/viewtopic.php?f=5&t=10342 |
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| Author: | Talya [ Sun Aug 25, 2013 11:39 am ] |
| Post subject: | Help me Nancy Drew this computer mystery... |
This is just out of curiosity, I have already fixed the problem, but how it happened is mind boggling to me, and I hate not solving a mystery. I have a networked hard drive box. Small, cheap, Linux-based EXT formatted DLink box with a lousy 4 TB of drive space on two drives (which I've set up in RAID-1 for redundancy, so 2TB working space) that I store my media on. In my music folders, I've ripped all my old CDs (and those few I still buy). I have all of Sarah McLachlan's CDs, and the other day, I discovered that all the songs ripped from just one of those CDs (Fumbling Towards Ecstacy) were corrupted, and while still the correct file length, played for all of 2 seconds each, making little electronic noise while they did, but nothing recognizable. All the other songs are fine. I'd blame the initial rip, except I've made an MP3 data CD that I had in my car a couple years ago from that folder, and it works fine. In fact, I "solved" the problem just by grabbing that CD and copying them all back to my NAS box, overwriting the originals. File corruption is nothing new. That doesn't surprise me. What surprises me is the specificity of the corruption. Random file corruption doesn't target files with metadata marking them as coming from one specific album. ONLY files ripped from one CD were corrupted, but at one point those files worked. This makes no sense to me. I hate things not making sense to me. |
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| Author: | Corolinth [ Sun Aug 25, 2013 4:53 pm ] |
| Post subject: | |
They were all ripped and stored at the same time, it's not out of the question that they'd have ended up in the same sector. When that sector went bad, it took that entire album. You may have some other files damaged that you just didn't notice because you haven't bothered to look at them. |
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| Author: | Diamondeye [ Sun Aug 25, 2013 5:39 pm ] |
| Post subject: | Re: Help me Nancy Drew this computer mystery... |
If they're in RAID-1, though, shouldn't the copy on the other disk have been ok? |
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| Author: | TheRiov [ Sun Aug 25, 2013 6:20 pm ] |
| Post subject: | |
Something to do with drm or copy protection? Software designed to kill files it thinks are in violation |
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| Author: | Rorinthas [ Sun Aug 25, 2013 8:46 pm ] |
| Post subject: | |
Computers do weird stuff, sometimes with no good explanation. Though "Blame DRM" seems like a good BOFH Excuse of the Day Calendar answer. |
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| Author: | Kaffis Mark V [ Sun Aug 25, 2013 10:15 pm ] |
| Post subject: | Re: Help me Nancy Drew this computer mystery... |
Diamondeye wrote: If they're in RAID-1, though, shouldn't the copy on the other disk have been ok? My money is on "the corruption occurred in transmission to copy the data TO the drives." Unless Talya's accessed the files uncorrupted since putting them there, which would blow my theory out of the water. But that theory would result in the corruption being mirrored. Alternately, it could be that it's only corrupt on one of the mirrors, and if she does an integrity check, it will discover that the mirrors differ on those files. |
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| Author: | Diamondeye [ Mon Aug 26, 2013 3:12 pm ] |
| Post subject: | Re: Help me Nancy Drew this computer mystery... |
I got the impression that she'd ripped the CD from those files, and therefore they were known to be good at one point in the past, but maybe I misunderstood. Also, if the files get corrupted on one drive in a RAID-1, shouldn't the second drive automatically give you the good files? How does that work? |
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| Author: | Talya [ Wed Aug 28, 2013 10:49 am ] |
| Post subject: | Re: Help me Nancy Drew this computer mystery... |
Diamondeye wrote: I got the impression that she'd ripped the CD from those files, and therefore they were known to be good at one point in the past, but maybe I misunderstood. Also, if the files get corrupted on one drive in a RAID-1, shouldn't the second drive automatically give you the good files? How does that work? One of the issues with RAID-1 mirroring is it doesn't actually protect you from file corruption. It protects you in the event of drive failure, but when data is corrupted for software reasons, there's a good chance it mirrors the corruption to the other drive. RAID-1 and RAID-5 are not backups. |
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| Author: | Vladimirr [ Wed Aug 28, 2013 12:37 pm ] |
| Post subject: | Re: Help me Nancy Drew this computer mystery... |
Talya wrote: This is just out of curiosity, I have already fixed the problem, but how it happened is mind boggling to me, and I hate not solving a mystery. I have a networked hard drive box. Small, cheap, Linux-based EXT formatted DLink box with a lousy 4 TB of drive space on two drives (which I've set up in RAID-1 for redundancy, so 2TB working space) that I store my media on. In my music folders, I've ripped all my old CDs (and those few I still buy). I have all of Sarah McLachlan's CDs, and the other day, I discovered that all the songs ripped from just one of those CDs (Fumbling Towards Ecstacy) were corrupted, and while still the correct file length, played for all of 2 seconds each, making little electronic noise while they did, but nothing recognizable. All the other songs are fine. I'd blame the initial rip, except I've made an MP3 data CD that I had in my car a couple years ago from that folder, and it works fine. In fact, I "solved" the problem just by grabbing that CD and copying them all back to my NAS box, overwriting the originals. File corruption is nothing new. That doesn't surprise me. What surprises me is the specificity of the corruption. Random file corruption doesn't target files with metadata marking them as coming from one specific album. ONLY files ripped from one CD were corrupted, but at one point those files worked. This makes no sense to me. I hate things not making sense to me. Take a look at one of the corrupted files in a hex editor, compared to one of the re-ripped versions, or even better download something like BeyondCompare and run a data compare. Do you see any particular patterns? Is the corrupted file a truncated version of the original (with zeros at the end)? Is there some data in it that might resemble another file format? Are the corrupted changes just seemingly random data? The fact that it only plays for a few seconds implies that your MP3 player can recognize one frame but none of the others, and even the data in that segment is wacky (maybe a corrupted bitrate or sampling frequency). It sounds like everything in just one directory got screwed up (assuming you sort out artists/albums by directory). Even if not, files ripped/copied at the same time are more likely to be in the same physical neighborhood on the HDD. Bad sector that the filesystem didn't correct? Assuming Windows, run a chkdsk /f in case? EDIT - And if I had read more of the thread, I would have seen Coro say basically the same thing. |
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| Author: | Stathol [ Wed Aug 28, 2013 2:59 pm ] |
| Post subject: | |
I'm not an ext guru, but... MP3 files are fairly large relative to your disk sector size, whatever that may be. It would take a fairly large defective region of the disk to corrupt them all. It's possible, but I wouldn't consider it very probable, even provided that the file blocks are all adjacent. My guess is that you're looking at some kind of inode corruption. That is, the file blocks on disk are not actually corrupted; rather, their inodes are pointing to the wrong blocks. Since all of the files were likely written at about the same time, it's likely that they have adjacent inode structures. Inodes are pretty small structures. One bad write or bad sector could easily fubar a bunch of them at once. This may or may not be something that fsck would detect. Semantical nonsense can nevertheless be syntactically correct. |
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