Re: LVM and disk failure
On Sat, Jan 07, 2006 at 11:02:25PM -0800, Mike Bird wrote:
> On Sat, 2006-01-07 at 22:15, Daniel Webb wrote:
> > On Sat, Jan 07, 2006 at 09:02:20PM -0800, Mike Bird wrote:
> > Well, yes, but supposing you *do* have a failure? Then what? Half the
> > filesystem is still there on the second disk, is it recoverable, and if not,
> > why not?
>
> You may get some of the data. You probably won't get all of it.
> I've had the great good fortune to have a group of bad blocks
> develop at a place on a drive where no data was currently
> stored, and I've lost data to bad blocks too.
>
> > I'm getting the impression that spanning volume groups with a logical volume
> > is a *very* bad idea unless the physical volumes are RAID.
>
> A VG built on two single drive PV's is twice as large but roughly
> half as reliable as a single drive. Depending upon the kind
> of data, that may or may not be a bad idea.
>
> Almost all of our VG's are built on RAID-1 PV's.
Yea, that seems to be the most common. I built a 6 drive raid 10 array
originally with 3 missing disks. That gave me the reliablity when I
eventually filled in the missing disks and was no worse off than
non-raid.
As far as recovering LVM data, you can use the vgscan --partial option.
It's supposed to do exactly as you describe.
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