On Tuesday 15 June 2010 10:00:03 [email protected] wrote: > > I am a PCLinuxos user and I have seen references to LVM here ( at SLUG) > > I have 3 drives LVM'd to give me 1.3TB of storage space on my server. > > The first drive of this set has died. > > I am guessing that by "LVM'd" you mean "concatenated together, no > redundancy", right? So, basically, you lost one disk and you have lost > (more or less) a third of the data under the file system, etc.
The stuff below is interesting and a reference, but this highlights my favourite rant: Seagate's 'ATA more than an interface' says multiple disks in a machine *will* result in a higher failure rate, maybe much higher. So raid is a less worse option than LVM. Heed the advice in slug talks about backup (Sorry Sonia and Margurite, I don't remember who presented them) It is possible, but not likely that *every* file on your disks is distributed over all 3 disks, so worst cast is that you lost 1/3 of every file you have. James > I further assume that "first" means "the one that contains the superblock", > as in the linearly first space on the disk. > > > I was wondering if any of you Guru's could suggest a method of getting > > any remaing data from the LVM drives, that is drive 2 and 3, that are > > left. > > I can identify three approaches: > > One: Get the "dead" drive working long enough to actually recover the > content from the file system with all the data around. > > That should work provided "died" means "has a bunch of bad sectors" rather > than "will not respond to SATA commands". > > > Two: Use something that scans the disk and looks for file content, then > extracts it. This is unlikely to bring much joy, but might be better than > nothing. > > I have used some of the tools packaged in Debian before, especially > 'testdisk', with reasonable success, on simple cases like "recover JPEG/RAW > images from CF cards". For a complex case like a 1.3TB file system, I > wouldn't hold much hope for getting a lot of content back. > > > Three: talk to the upstream file system developers, and see if they can > help identify a mechanism that might recover data without the first chunk. > > > I suspect those are in decreasing order of what you get back, and other > than the first that will be "very little". > > > Er, and there is another option: pay a data recovery company to do > this. It shouldn't cost more than a few thousand dollars for a fairly > simple case, and might have a better recovery rate than the alternatives > if, say, disk one *isn't* responding, but they can get it back talking for > a bit without too much trouble. > > > I have tried rebuilding the set, wg0, but the system want to reformat the > > drive wg0, just created. Is this formatting going to format the real > > drives and rather that just the LVM component? > > All LVM does, in this case, is rewrite the "write" command so that it talks > to the appropriate bit of the underlying physical device. So, yes, > because there is no difference between the two. > > > > Anyway, for the future: if you concatenate drives, which is all that LVM > does, you increase the chance of total data loss in your system by the > number of devices; in your case — three disks, triple the chances you > lose. > > So, the take-away lesson is that if you intend to do this take one of these > three approaches: > > 1. Format each device as a separate file system, rather than concatenating > them, so that loss of one device only takes away one set of data, not > all three. Penalty: you now have a PITA job using all that space. > > 2. Keep good backups, so that when (and it is "when", not "if") you lose a > device you recover much more gracefully. > > 3. Use some sort of redundancy: software RAID is a pretty decent choice, > and is pretty inexpensive these days. Certainly, I bet that the extra few > hundred dollars for a second set of disks is less than the cost of trying > to recover all that data. > > > Um, and sorry: it sucks that you are now probably going to lose all that > data. > -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
