CentOS - Apr 2007 - LVM & Softraid & expansion

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!
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.centos.org/pipermail/centos/attachments/20070401/39c3f9a8/attachment-0004.html>

Cen Tos 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?
yup, pretty much thats how it works.

In IBM AIX (where LVM kinda came from), the soft raid and volume 
management is rather tightly integrated, but in linux, its seperate.

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!
>
>
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos
>
>