[CentOS] LVM & Softraid & expansion

Gordon McLellan gordonthree at gmail.com
Sun Apr 1 15:43:51 UTC 2007


I haven't evaluated centos 5 beta yet, so I don't know what its kernel
supports.  'The' linux kernel supports resizing (grow only) of
softraid 5 arrays.  Combine that with LVM2, which supports hot-growth
and a file-system that supports some sort of growth (I'm using xfs),
and you have a very flexible and expandable configuration.

I'm not so sure you "need" to resize a raid 5 array with lvm, but it
makes expanding the storage cheaper.  Without resize, to expand you
need to buy enough drives to form a new array, define it as a PV and
extend one or more VGs to it.  With hot grow, you just add one (or
more) drives, resize the array and expand the underlying PV (and
VGs)..

Maybe someone else has a simpler method?  This looks like a lot when
you write it out, but its just two or three commands and a lot of
patience.

Gordon

On 4/1/07, Cen Tos <centos.admin at gmail.com> wrote:
> I've been reading the RHEL 5 manual/guide linked from centos, and the idea
> of LVM with expandable partitions seems like a great idea (yes duh why else
> would it exist if not?). Although the documentation shows a screenshot of
> how the final setup would look like with LVM & RAID together, it doesn't
> actually gives the step.
>
> 1. Am I correct in thinking it should be done in this way
> - setup Softraid
> - setup LVM on the raid partitions
>
>
> Secondly, LVM allows expansion of the LVM group when we add a new drive. But
> with softraid, how will this happen? Searching around does not turn up any
> guide on this. Am I correct in thinking I must always add new drives in
> pairs (for Raid 1), create a new softraid partition then assign this new
> partition to the LVM group?
>
>
> Thanks!
>
>
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