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Re: Question about LVM and RAID

rainer wrote:

Kanwar Ranbir Sandhu wrote:
Hi All,

I have an external drive cage which has been configured with two
separate RAID 5 arrays.  I then used LVM to create two PVs, and then
added the volumes together under one VG.  The whole shebang is mounted
on one file system (/srv).

What would happen if one of the RAID arrays failed (e.g. two drives die
in RAID 5 array 1)?  Would the data be safe, would I lose all data, or
would I just lose the data that was on the failed array?

I believe I would only lose the data on the failed array, but a friend
believe I would lose the whole lot.

Thanks in advance!



> Hi,
> I suppose you have only made a JBOD with LVM - no further RAID0 or such.
> With JBOD, at least the data on the left RAID5-set should be safe. The
> data on the failed array and the bits and pieces which were on both
> arrays would be lost. Fragmentation and the size of data could be an
> issue - e.g. a 200 GB file on 2 x 160GB arrays would mean more than half
> is lost... ;(
> I think your friend meant you had made a RAID0 above the RAID5-sets,
> which would indeed mean the whole thing would be lost.
> Regards,
> rainer

To add to this.

A RAID 5 array is dependent on the number of drives where the data is spread across. If there are 3 drives, then two failures is more than enough. If you have 6 drives, then two drives may be okay.

It would be more useful to explain the RAID setup with the hardware, number of drives per RAID and how they are configured.

Robin Laing

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