Erik Mouw wrote:

On Fri, Feb 10, 2006 at 10:01:09AM +0100, Mirko Benz wrote:
Does a high speed NVRAM device makes sense for Linux SW RAID? E.g. a PCI card that exports battery backed memory.

Unless it's very large (i.e.: as large as one of your disks), it
doesn't make sense. It will probably break less often, but it doesn't
help you in case a disk really breaks. It also won't speed up an MD
device much.

Could that significantly improve write speed for RAID 5/6 (e.g. via an external journal, asynchronous operation and write caching)?

You could use it for an external journal, or you could use it as a swap
device.

Let me concur, I used external journal on SSD a decade ago with jfs (AIX). If you do a lot of operations which generate journal entries, file create, delete, etc, then it will double your performance in some cases. Otherwise it really doesn't help much, use as a swap device might be more helpful depending on your config.

What changes would be required?

None, ext3 supports external journals. Look for the -O option in the
mke2fs manual page. Using the NVRAM device as swap is not different
from a using "normal" swap partition.


Erik



--
bill davidsen <[EMAIL PROTECTED]>
 CTO TMR Associates, Inc
 Doing interesting things with small computers since 1979

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