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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!

Regards,

Ranbir

> 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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