Gvinum RAID5 performance

[Brad Knowles]

At 9:55 AM +1100 2004-11-01, <freebsd at newmillennium.net.au> wrote:

>  Now, running a dd from a plex gives me less performance than running a
>  dd from one of the subdisks, even though the array is not running in
>  degraded mode.

	Right.  This is RAID-5.  It is used for reliability, not 
performance.  The entire stripe has to be read at once and written at 
once, for any operation involving that stripe.

	If you want maximum performance, try RAID 1+0 (make sure to 
stripe the mirrors and not mirror the stripes).

>  On a final note, I'd like to implement the ability to grow RAID5 plexes
>  - any suggestions on where to start?

	This is a more complex issue than you realize.  If you want to 
contribute code to perform this operation, I'm sure that the project 
would be more than happy to receive them in consideration for 
inclusion in the gvinum code.

-- 
Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.