Subject: Re: SATA software RAID-inkernel vs hardware
To: None <,>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: tech-net
Date: 10/26/2005 12:50:55
> [...Linux...] people say kernel raid is as good as any BIOS raid.
> Would that be true for NetBSD as well?

Better, in my (admittedly rather limited) experience.  At work, we had
a machine with a "hardware" (firmware, really) RAID card in it.  We saw
repeated hangs with it.  On investigating, I found that everything was
waiting for vnode locks.  After using ddb to chase through "this
process is waiting for lock A, who holds lock A, it's process B;
process B is waiting for lock C, who holds lock C, it's procss D; ..."
a few times around, I invariably found a process that was blocked
waiting for an I/O request to the raid device's driver to complete.

After three or four such hangs, I yanked the RAID card and popped in a
regular SCSI card and switched it all over to RAIDframe.  The hangs
completely disappeared.

We also have another machine which is using "hardware" RAID with no
problems, but the RAID card is from a different manufacturer.  So my
take on it is that "hardware" RAID is "might be fine, might lose big",
whereas RAIDframe basically Just Works.  Just don't swap to it. :)  (Or
has the deadlock-against-itself bug been fixed by now?  Probably....)

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