First, thanks to everyone for the helpful responses.

On Fri, Mar 12, 2010 at 3:36 AM, Kristleifur Daðason
[off-list ref] 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
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html