  Upgrading Overloaded (HSD) Disk I/O? 
 The Question is:
 
How to replace disk in VAX DSSI cluster and improve performance?
 
I've a VAX 4505 cluster with 2 HSD10 &amp; 2 R400X. The current cnfig is that each
 HSD10 has 7 disks in it and 2 of the them is mirrored by Volume Shadow as
 DSA1($4$DUA11&amp;#65292;$4$DUA12)&amp;#65292; and DSA2($4$DUA21, $4$DUA22),
 separately. Now it suffers a  per
formance problem(DIO is about 70, IO queue is 3).
 
1) I want to replace the 4 disks with larger disk to get more capacity. What's
 the detail commands and procedure?
2) ay I get performance improvement by this way?
2.1) create a stripeset with the 2 new disks in each HSD10, and create 2
 partitions in the  stripeset.
2.2) Mirror one partition in a HSD10 with the other one in the ther HSD10 by
 Volume Shadow?
3) How to keep the disk device names unchanged after the replacement so that
 all appliactions  can work as before without any code or configuration
 modification?
 
 
 The Answer is :
 
  The OpenVMS Wizard would tend to replace the entire configuration, as
  the central performance limit is likely that of the DSSI (and, for that
  I/O traversing it, the Q-bus), and as the performance of the VAX 4000
  model 505 is itself rather glacial by current system performance
  standards.
 
  DSSI has the performance characteristics of SCSI-1, and that limit will
  very likely throttle aggregate I/O performance here regardless of the
  particular disks installed.
 
  An I/O queue depth of 3 indicates that your disk I/O is overloaded --
  the OpenVMS Wizard generally considers a depth average above 0.5 to be
  bad, as that indicates half of all I/O is waiting.  Your queue depth
  of 3 indicates I/O saturation, with all I/O waiting.
 
  Depending on locality of reference and on the I/O load, you might
  want to look at what is generating the I/O load and at improving
  the host-based caching -- adding physical memory.  A performance
  evaluation based on the performance manual might find a glaring error
  in the configuration -- overly small working sets forcing excessive
  paging I/O, for instance.  But it is also as likely that the current
  I/O requirements and system hardware are simply overloaded.
 
  Please contact your hardware reseller or sales representative for
  assistance in configuring the storage upgrade, or (likely better)
  in replacing the current system hardware configuration with a newer
  one.
 
 Answer written or last revised on  17-DEC-2003 
