Two questions regarding the CERC SATA1.5/6ch RAID controller

David Kinnvall david.kinnvall at alertir.com
Sun May 9 06:47:00 CDT 2004


Hi all,

Having recently bought two new Dell servers, one 700 and one 750,
for use as disk-based backup servers, I have two questions regarding
the CERC SATA1.5/6ch RAID controller (optional for both) that they
came with.

For the 750 there is no problem, since with only two drive bays I
opted for a RAID1 config with 2 250GB drives. Performs adequately.

For the 700 I have additional storage requirements, namely 2*250GB
effective storage, which resulted in a RAID5 config with 3 250GB
disks. Performs NON-adequately, unfortunately. It seems this card
is particularly bad at the additional RAID5 overhead, causing write
performance to drop to about 1/10th of the above RAID1 cousin...

How to solve? My (naive?) primary plan is do exploit the fourth, so
far unused, drive bay of the 700 for a fourth 250GB disk, and migrate
the RAID5 array to a RAID10 array, spending an additional disk but
hopefully gaining back (most of) the performance loss. Realistic?

Now, my questions:
- Can the CERC SATA1.5/6ch available for the 700 handle RAID10 ?
- Can I migrate the already created RAID5 array to a RAID10 array
   "online", without starting from scratch? If possible, what are
   the steps in either the BIOS screen(s) or (preferably) in afacli?

The docs for the CERC SATA1.5/6ch, which I believe are available
at http://docs.us.dell.com/docs/storage/cerc/index.htm, seem to hint
at the possibility, but do not go into any details. The tech info
for the 700 does not mention RAID10; only 0, 1 and 5. Argh...I hate
conflicting docs... :-/ Also, the Swedish Dell tech support has not
been able to conclusively answer the above questions either way...

Anybody able to help me with this? I would greatly appreciate it!

Thanks,

David




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