Slow RAID IO on PE2970

John LLOYD jal at mdacorporation.com
Fri Mar 13 12:27:04 CDT 2009


> > I would recommend you reconsider using RAID5 and 3 disks to 
> obtain the
> > capacity of 2 disks -- RAID1 is a better choice here, and leaves you
> > one
> > disk spare.
> Many thanks for that. It makes a good deal of sense.
> 
> We have a 4th drive waiting to go into that box so would a 
> RAID 10 be a better answer in terms of performance? Are we 
> close to the limit of SATA drives irrespective of the array 
> type we use?

Yes, RAID10 is almost always better than RAID5 for performance, and
certainly this is true during a RAID rebuild.  It is not really
expensive as disks are cheap.  As the arithmetic shows, you have a lot
of available  capability in the SATA disks if you can avoid the RAID5 IO
overhead.

> 
> How much performance would we get by moving to SAS drives and 
> could the Perc5i have 2 arrays of 1 SATA and 1 SAS (all 
> internal drives) as we're unsure if can have mixed array types?
> 

Yes we have successfully mixed SAS and SATA on the same PERC5 (and
PERC6).  It is supported, although you cannot order a server that way
from Dell you can add disks later.

For us the 15k rpm SAS disks are noticeably faster.  But you can't get
1TB SAS disks, so eventually you have to decide if you need speed over
capacity.


--John
 



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