Re: Resize RAID-0?

["Patrick J. LoPresti" <lopresti@gmail.com>]

First, thanks to everyone for the helpful responses.

On Fri, Mar 12, 2010 at 3:36 AM, Kristleifur Daðason
<kristleifur@gmail.com> wrote:
>
> I agree with others on the list - I believe that LVM will perform well
> as a flexible stripe wrangler on top of mdadm arrays. For instance
> some LVM striping over mdadm parity-based stuff underneath.

I made a typo in my original post, so let me clarify.  In my
configuration, I have a pair of dual-channel FC HBA cards.  I
currently have three hardware RAID-5 chassis connected to three of the
HBA channels, and I am using Linux md to perform RAID-0 striping
across the channels.  This gives me very high performance -- 800
MiB/sec sustained reads and writes, for hundreds of gigabytes, using
XFS -- at very modest CPU utiliziation.

What I want is to connect a fourth, identical hardware RAID chassis to
the fourth HBA channel and then re-stripe the md RAID-0 across all
four units.  I now understand that this is not currently supported.

> Do you want to add a whole new stripe device, so changing the
> coarse-scale layout, or grow the underlying data containers?

New stripe device.

> As you are running striped, I assume that the data is either
> perishable or backed up.

My data is all reproducible.  (The system spends its time processing
large volumes of data that originated somewhere else.)  We are using
underlying RAID-5 chassis to improve MTBF, not to prevent data loss.

> I'd suggest you look into moving to LVM.

Thanks to Michael Evans and to you for this suggestion; I will investigate LVM.

Thanks once again to everyone who responded.  The world of Linux RAID
may be "gas-lit and magical", but in many ways the support is superior
to any commercial product I have seen.

 - Pat
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