PERC 5/i question

Ben Scott dragonhawk at
Mon Dec 11 21:40:00 CST 2006

On 12/11/06, Matt Richardson <marichar at> wrote:
> Is there an advantage to running software raid vs hardware raid?

  Software RAID is portable between hardware.  Hardware RAID is
portable between software.

  In other words: Using Linux software RAID, you can move disks
between controllers/machines/etc and still access the same disks.
Using hardware RAID, you can boot two different OSes (or different
versions of LVM, etc.) and still access the same disks.

  Hardware RAID can give you a performance benefit if your machine is
busy running other tasks.  Software RAID can save you money if your
CPU/RAM/bus/etc are lightly loaded and can spare the resources.

  In my experience, hardware RAID tends to be a bit more robust in the
face of failures, but that might just be coincidence.

> Is it possible to configure a PERC 5/i (in a PE2950) to not act as a
> raid controller?

  You can create a Logical Drive (LD) for each Physical Disk (PD) on
the controller.  That effectively gives you one-to-one between LDs and
PDs.  I'm not sure what overhead you'll incurr on the controller,
though.  It might be you still pay the performance penalty of running
through the RAID firmware and processor.

> This is all new to me as I used hardware raid on my
> previous PEs, no lvm.  However, I like the flexibility lvm offers,
> especially with xen guests.

  You can run LVM on top of hardware RAID.  LVM for storage
management, hardware RAID for reliability.  I've done this before;
works well.

-- Ben

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