RAID controller question...

[Christian Worley]

Michael Pearl wrote:
> 
> Have you looked at DPT's controllers?  I don't have performance numbers,
> but I am currently running RAID-5 using a 2144UWR with RedHat 5.0.
> 

Michael,

Your system is in use, so performance testing may not be possible...

But, if you can destructively test your system, try (assuming your
raid is /dev/sda):

	time dd if=/dev/zero of=/dev/sda count=65536 bs=65536

That will destroy any file system on /dev/sda, so don't do it on
anything but a new, destroyable, system (i.e., where you haven't run
"mke2fs" yet).

A similar test via a file system, assuming it's mounted on /dev/hd,
would be

	time dd if=/dev/zero of=/mnt/hd/foo count=65536 bs=65536
	rm /mnt/hd/foo

This would not be a destructive write test, but would include the
overhead of the file system and create a 4GB file.  Make sure to
delete the file: if you run this test twice without deleting the file
in-between, then you'll also measure the time for the file system to
delete such a file, which is not insignificant.

A read test, that won't destroy the system and won't be worst case
(because it won't show the overhead of calculating RAID-5 parity
stripes) would be:

	time dd if=/dev/sda of=/dev/null count=65536 bs=65536

But that figure would be interesting too.

I test performance using the raw device since this uses only their
driver and not the file system overhead, even though that overhead is
negligible.  Given such a configuration, comparing RAID-0 to RAID-5
numbers shows the overhead brought on by the board and not the PCI bus
nor OS.

I've been told by the manufacturer that my test is not valid, since
it's not random (not reading and writing from random blocks) as normal
use would be.

I'd like to know of what real performance numbers (using the "dd"'s,
above) different RAID boards get.

Chris
-- 
  When I die, please cast my ashes upon Bill Gates
   --for once, let him clean up after me!