Clive Just ([log in to unmask]) wrote:
: Does anyone have any experience with both Model 20 HA Disks and disks
: mirrored with Mirror/IX.

: System is currently KS979/400 running 5.5. We are looking to to upgrade our
: disks and have been warned that Model 20's are designed for availability not
: performance and that software mirroring is considerably faster.  This
: certainly goes against my intuition but where are the facts?

: If we went Model20 then we would only use RAID1 (mirroring) not RAID5 - does
: that swing the balance at all?

"It depends" Both devices are capable of good performance but
if you are almost read I/O bound today then Mirror/iX might give you
slightly better performance. If you are CPU bound today Mirror/iX uses
slightly more CPU because of the double writes but it can read from both
discs at the same time. The Model 20 in raid 1 is a good HA
solution, especially if you need it for the system domain drives because
Mirror/iX doesn't work for the system domain volume set. Mirror/iX also
has some CPU overhead during the recovery process(say after a SA) that
the Model 20 doesn't. The Model 20 drives could be controller bound since
they may be all connected to the same interface card in the HP3000. You
have a issue in that interface card is a single point of failure in the
Model 20. Also, raid 1 is the best Model 20 solution for the HP3000.


You pick

  Lots of volumes     favors multiple Model 20s because of Mirror/iX
                      Recovery time
                      (about 1/2 hour for six disks at a time)
  OLTP READ intensive
                        favors Mirror/iX because of dual I/Os
  CPU bound and Write intensive
                        favors Model 20s because of slightly more CPU
                              overhead to do two writes
  Single point of failue on Model 20s interface controller
                      favors Mirror/iX because you're supposed to put the
                    mirrored volume pairs on different disc controlers
  Cost ?????

  Of course this all assumes you don't go from 4gb fw highperformance drives
  to 18gb fw highperformace drives at the same time and your I/O rate is
  high.


                                                                                               "Your actual mileage may vary"



--
         ___
        /  /            Stephen F. Macsisak :Performance Consultant
HEWLETT/hp/PACKARD      Commercial Systems Division
      /__/              [log in to unmask] :(408)447-5851 (or MOONEY N201PC)