RAID controller question...

[Eric Billings]

> which I think will work, but can't find pricing on either and am not
> sure if LINUX drivers exist for each.  The controllers are:
> 
> 	AMI MegaRAID® Ultra2/5 (Series 438)
> 
We are currently running the AMI MegaRAID UltraGT under Linux 2.0.31 with
a vendor-supplied driver.  It is configured as RAID-5 with 8 18GB drives
spread across the 3 channels of the controller.  It has 128MB on-board
cache.  Performance with this is fine - not great.

For burst writes and reads we are measuring 20-30MB/s for files < 50K that
are cacheable.  Sustained writes to disk are about 2.2MB/s with 8 disks in
a single logical volume and data-striping enabled for files > 1GB.

We are currently testing data recovery.  This takes a while because
loading the disk with >100GB of data takes more than 12 hours.

CAVEAT EMPTOR: Hardware supported RAID requires that you can get to the 
controller's code to rebuild a lost disk.  This means that you must take 
the system down and reboot to get to the PCI controller during the boot
sequence.  This eliminates advantages such as hot-swap and keeping the 
host node accessible during the rebuild process.  At least so far...

- Eric

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Dr. Eric Billings                                Voice: (301) 496-6520
Laboratory of Biophysical Chemistry               FAX:  (301) 496-2172
National Institutes of Health            email: billings@helix.nih.gov
LoBoS: Lots of Boxes on Shelves              http://www.lobos.nih.gov/
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