"Gerald C.Catling" <[email protected]> writes:
> 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.
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.
Daniel
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