Subject: Re: RAID In general (Re: Hot Swappable IDE Kits)
To: Greg Oster <>
From: Manuel Bouyer <>
List: current-users
Date: 04/17/2003 20:29:51
On Wed, Apr 16, 2003 at 01:55:52PM -0600, Greg Oster wrote:
> > 
> > Yes, software raid is cheaper to acquire.  But it's slower
> Do you have pointers to any specifics on this?  I'd be quite interested in 
> seeing benchmarks for "modern" hardware... (preferably using the same disks 
> on the same hardware)

This is not true, at last for external boxes connected to a SCSI port.
For example, in my DS20 I can get 50MB/s (though the filesystem, more from
the raw device) out of a raid-1 built from 20 disks spread over multiple
SCSI UW channels. An external box would be limited by the SCSI bandwidth 
(something like 35MB/s in this case). Yes, the external raid box could
be connected to a Ultra320 controller. I could as well use 20 U320 drives
connected to 4 U320 controller, and it would still be faster.
Also, in my setup I can have 20 * 256 = 5120 outstanding commands.
With an external RAID this would be limited to 256.

hardware RAID PCI controllers don't have the limitations of external raid
boxes, as they have mutliple channels. So they should be at last as fast as
software RAID.

Manuel Bouyer <>
     NetBSD: 24 ans d'experience feront toujours la difference