[nmglug] sfotware raid more fragile than plain partitions?!??

[Tim Emerick]

The best hardware raids utilize a battery on the card.  I think that's for flushing on-board cache to the disk in the event of a power failure.  I'm imagining that a good software raid should also have a battery via a UPS.

----- Original Message ----
From: Aaron <eunichs at boim.com>
To: NMGLUG.org mailing list <nmglug at nmglug.org>
Sent: Wednesday, May 16, 2007 5:57:07 AM
Subject: [nmglug] sfotware raid more fragile than plain partitions?!??


Is it possible that LINUX software RAID (1,4,5,6) is actually a LOT
less reliable than a plain old partition, or perhaps even LVM?

I have had some corrupted 'dirty' RAID volumes, TWO at a time...
enough to kill a RAID5.

Journaling filesystems do a pretty good job of limiting damage
from dirty shutdowns.
I am afraid that software RAID (mdadm) may not have this property.
Is it possible that a simple trip over the power cord could cause
MULTIPLE parts of a RAID to become 'non-fresh', causing
one to loose the entire RAID?   Even if a fsck on the overlying
filesystems might recover most if not all of the data?

How much might I have to spend on a hardware RAID to reduce
the likelihood of this problem?
How many hours might I spend learning about detailed operations
of hardware RAID to recover from such a partial corruption?

I am really questioning weather or not RAID makes sense at all.
Perhaps I should stick to asynchronous mirroring for robustness,
and LVM for striping.

             aaron

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