RE: RAID5 parity sets

["Allen, Stuart" <sallen@xxxxxxxxxxxx>]

What you do will be determined by the type of disk already on your system.
Parity sets must be made up of like drives.
Spreading parity over 8 rather than 4 disks is the optimal solution - it
offers better performance - parity writes/reads take place over more disk
arms.  The system will use this if possible, otherwise will go to 4.
By the same token, i'd assume that keeping each parity set down to 8 drives
each would be optimal as it would have the minimum amount of parity data on
the 8 drives.

In your situation though, 2 sets of 10 would be the best solution - while
you could concievably go to 8,8,4 this would mean running 16 disks off one
IOP, and only 4 off another...

Regards,
Stuart
                                     
Stuart Allen
European Systems Analyst
Fellowes

mailto:sallen@fellowes.com


> -----Original Message-----
> From: Graham, Ed [SMTP:EGraham@mvh.org]
> Sent: Thursday, May 18, 2000 9:17 PM
> To:   'MIDRANGE-L@midrange.com'
> Cc:   Graham, Ed
> Subject:      RAID5 parity sets 
> 
> I posted same question(s) on AS/400 Forum BBSN today. I have two existing
> parity sets of 5 and 7 drives each(IOPs are 2748 and 6533 on a 720-2061).
> I
> want to add 8 more drives (6713s). I believe that I can get full capacity
> from additional drives by adding them to existing parity sets so that each
> would have 10. Does this make sense? Current sets have parity spread
> across
> 4 drives. I've seen some parity sets on my other systems that have parity
> spread across 8 drives. Is this determined by the system? For a 10 drive
> parity set, what is the optimum setup? Is there a reason that I should
> keep
> parity sets no larger than 8? I appreciate any suggestions.
> 
> 
> 
> 
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