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Re: [linux-lvm] Drive gone bad, now what?



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On Tue, 28 Oct 2003, Gert van der Knokke wrote:
> John Stoffel wrote:
> >Gert> I didn't expect lvm to restore the missing data, I guessed it
> >Gert> would just let me access the rest of the data.
> >
> >At this point, you have to think, how can my filesystem cope with the
> >loss of a 60gb chunk of data in the middle (start or end even) of the
> >300+ gb of data?  There's all sorts of meta-data and true data which
> >is now gone, and re-building the filesystem into a consistent state is
> >really impossible.
> >
> Hmm, and so I think LVM still needs a warning label :-)

Maybe, in the same way that McDonald's now feels compelled to remind its
customers that hot coffee is hot.  I don't recall anything in the
description of LVM which suggests that it provides redundancy or other
data-protection mechanisms.  RAID, regular backups, and retention of
distribution media are still required if you value your data.

> I wonder why LVM doesn't work the other way around:
> Create filesystems on several disks and then concatenate these to the
> outside as one large filesystem. This way if one drive goes bad you can
> always individually mount the drives and use the data.

man mount

> >If you are looking for a large/cheap/reliable bunch of storage,
> >instead of mirroring, you might want to think about RAID5 instead.
> >
> No, what we're looking for is an 'expandable as needed' filesystem and
> this is what LVM pretends to be.

That's what it *is*.  You can slice and dice your physical storage and
recombine as needed.  Do that to redundant physical storage and you have a
highly reliable expandable storage stack.  Do it to a simple concatenation
of cheap disks and you have a cheap failure-prone expandable storage
stack.  Expandability and reliability are orthogonal, and you use separate
tools to provide them.

- -- 
Mark H. Wood, Lead System Programmer   mwood IUPUI Edu
MS Windows *is* user-friendly, but only for certain values of "user".
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