PERC RAID 5 config parameters

jason andrade jason at rtfmconsult.com
Tue Mar 25 16:46:01 CST 2003


On Tue, 25 Mar 2003 rb at raphinou.com wrote:

> Hi,
>
> two little questions about configuring the RAID 5:
>
> -the CCCU proposes two options for creation: via scrub or via clear.
> What's the meaning exactly of both?

"CCCU?"

scrub means that the controller goes off and does some consistency
checking that all elements of the raid are actually in sync.  you
will occasionally lose a disk and replace it and will see a message
about "container scrubbing" which is the rebuild/recheck process
happening.

so i guess in the context of creation it will be slower to create
via scrub but this does some extra testing for you at creation time
which could flush out a potential problem.

clear would be the faster method (by deduction) where the bios simply
wipes the disks and then puts them together as raid5.

> -What are the parameters to look at when choosing the chunk size? I
> realise this is a more general question. Any good pointers welcome ;-)

it depends on your application set and system tuning can be a wonderfully
arcane thing with this value :-)

my first guess/rule of thumb would be if you have large files then chose a
larger chunk size.  if you have a database going on the filesystem then it
might be optimal to pick a disk chunk size that matches the database read
or write segments.

regards,

-jason




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