Ask Slashdot: What's a Good Tool To Detect Corrupted Files?

Volanin writes "Currently I use a triple boot system on my Macbook, including MacOS Lion, Windows 7, and Ubuntu Precise (on which I spend the great majority of my time). To share files between these systems, I have created a huge HFS+ home partition (the MacOS native format, which can also be read in Linux, and in Windows with Paragon HFS). But last week, while working on Ubuntu, my battery ran out and the computer suddenly powered off. When I powered it on again, the filesystem integrity was OK (after a scandisk by MacOS), but a lot of my files' contents were silently corrupted (and my last backup was from August...). Mostly, these files are JPGs, MP3s, and MPG/MOV videos, with a few PDFs scattered around. I want to get rid of the corrupted files, since they waste space uselessly, but the only way I have to check for corruption is opening them up one by one. Is there a good set of tools to verify the integrity by filetype, so I can detect (and delete) my bad files?"

Comments

AppleScript

[noh8rz3]

An AppleScript / Automator script can step through files on a hd, open them, and catch a thrown error if the open fails. Tis sits a good automated way to glad the bad ones. Not the fastest method, but it could run at night.

you seem to be surprisingly ok with the fact that your computer crashed and all your documents and media were corrupted, as was your backup. I would have been beside myself. Hulk smash! Please let us know what different set ups you're exploring to avoid this.

Re:AppleScript

[jasno]

Here's what I did when I realized my mp3 collection on my Mac was slowly dying:

find -print -exec cat {} > /dev/null

it takes a while, but for files with ioerrors you'll see a warning printed after the file name. Put the output in a file and you can use grep(the 'B' option comes to mind) to get a list of the bad files.

The sad thing is that Time Machine didn't seem to notice that the files were bad, so now the files are gone forever. Disk Utility didn't help.

Shouldn't there be a way to find bad blocks on OS X? I looked around and all I could find were commercial products.

md5sum

[sl4shd0rk]

or sha1sum if you prefer. Automate in cron against a list of knowns.

eg:
$ md5sum /home/wilbur/Documents/* > /home/wilbur/Docs.md5
$ md5sum -c /home/wilbur/Docs.md5

A lot of corrupt files?

[19thNervousBreakdown]

That seems very strange--the only files that should really be corrupted, unless something extremely rare and catastrophic happened, are the ones that were being written when power went out, or were cached. And even then, a flush usually flushes everything, or at least whole files at once, or areas of disk. Is the partition highly fragmented or something?

I know this doesn't do much for your question, but that kind of failure mode is almost exactly what filesystems do their damnedest to avoid. HFS+, being journaled, should be even more proof against, well, exactly what happened to you. Maybe the Linux driver is poor, but man, if you got silent data corruption on a multitude of files that weren't even being written, that's really bad and the driver should be classified "EXPERIMENTAL" at best, and certainly not compiled into distros' default kernels.

To answer your question, I don't have experience with any tools (I automate my backups, and any archival files go on a RAID volume that does a full integrity scan nightly), but once you find one, you should separate your files into two categories--"must be good", and "can be bad". The "must be good" files (serial #s, source code, etc.), you hand-check, so you know for certain that every one of them is good. It'll also motivate you to replace them now, instead of later when replacements will only get harder to come by. The "can be bad" files (music, pictures, etc.), you do the automated check on and then just delete as you run into ones that the check missed. This has the advantage of concentrating your effort into where it's useful. If you try to check all of your files, you'll just burn out before you finish. You may even want to do more advanced triaging, but you'll have to come up with the categories and criteria there. The main thing is, split this problem up.

Re:Newbie question hour?

[loftwyr]

mplayer can detect corrupted movie and audio files find . -name '*.mov' -exec mplayer -msglevel all=6 -speed 100.0 -framedrop -nogui -nolirc -cache 8192 -tskeepbroken -ao null -vo null {} \; | grep Warning! > $1.txt Change the *.mov as appropriate.

Get Rid Of Paragon!

[Lord_Jeremy]

Alright now I'm afraid I can't help with your verify problem but I do have one piece of solid advice: get rid of Paragon HFS immediately!

It is a truly shoddy piece of software that as of version 9.0 has a terrible bug that will cause it to destroy HFS+ filesystems. Google "paragon hfs corruption" and you will see many many horror stories from people who just plugged a Mac OS X disk into a Windows machine w/ Paragon HFS and then discovered the entire filesystem was hosed. In my dual-boot win/mac setup I replaced my copy of MacDrive with a trial version of Paragon HFS 9.0 from their website and every single one of the six HFS+ disks I had connected internally were damaged. Disk Utility couldn't do a thing and I had to buy a program called Diskwarrior to even begin to recover data. I ended up losing two disks worth of files anyway.
http://www.mac-help.com/t12137-opened-hfs-drive-win7-paragon-hfs-now-wont-boot.html
http://www.wilderssecurity.com/showthread.php?t=299306
http://hardforum.com/showthread.php?t=1677099
http://www.avforums.com/forums/apple-mac/1509344-hfs-super-block-not-found.html

whew! Anyway the pain I went through after that software very nearly ruined my life was so great, I don't want it to happen to anyone else. According to their own website 9.0 has this awful bug but they fixed it in 9.0.1. Evidently the trial download on the main page is still for version 9.0 and still has the disk destroying bug! Any software company that releases a filesystem driver with this terrible a bug (not to mention the numerous reports of BSODs and other relatively minor problems) clearly has terrible quality assurance and simply can't be trusted.

Re:Get Rid Of Paragon!

[macraig]

Having nothing at all to do with Paragon (not that I'm a fan of the company otherwise), I had a very similar disaster occur with an external eSATA 5TB RAID 5 enclosure. It's one that uses an internal hardware RAID 5 circuit and doesn't require port multiplication, so when connected it appears to the host as a single large volume. At the time I was swapping it between a Linux (Ubuntu) system and a Windows 7 system; it was of course configured as GPT. Eventually I connected it to the Windows 7 system and during boot Windows declared there were problems and initiated chkdsk. Chkdsk ran for more than 18 hours and when it was done, most of the files in the volume were hopelessly corrupted. Upon detailed inspection, I found that blocks of all the files were swapped and intermingled, as if something had made a jigsaw puzzle out of the MFT and couldn't reassemble Humpty Dumpty. Was it chkdsk itself that caused the damage? Was it the swapping between two machines and operating systems (both GPT compliant)? I suspect it was actually caused by chkdsk, but could never prove it.

Photorec is great BUT

[rduke15]

Indeed, I used photorec/testdisk to recover mp4 files after they had (all) been accidentally deleted from an HFS+ partition.

But when I first started it in it's default mode, it "found" only rubbish, breaking up the actual mp4s into a mess of .doc, xml, jpg, .whatever files, including totally broken .mp4s.

When I restarted it after configuring it to only look for .mov/.mp4, it did a fantastic job, and as far as I know, all files could be recovered. Of course, that was made easier by the fact that I knew that all the files which needed to be recovered were .mp4.