HP OpenVMS Systems

ask the wizard
Content starts here

Increasing Application I/O Performance?

» close window

The Question is:

When running an application such as SAS, which uses asynchronous Direct I/O, on
 an AlphaStation 500au, against locally attached UltraSCSI disks (5 disks,
 software RAID 0, FWD SCSI bus), read/write performance is poor compared with
 other similar OS's and d
oes not respond to changes in the blocksize being transferred.  The CPU
 generally sees about 50% utilization, the disks are observably in intermittent
 use (access lights flash).  The SAS job is the only process on the system.
1) is it possible that the Storageworks RAID driver "packetizes" or otherwise
 generates multiple small synchronous I/O's, rather than single large
 asynchronous I/O's?
2) are there other tuning or hardware parameters which might result in low-rate
 synchronous I/O on this system?

The Answer is :

  Unfortunately, a specific answer will require detailed knowledge of
  the application and particularly of the application I/O activity and
  I/O processing.  Potential areas where performance could be improved
  involve the application file I/O, process quotas, system parameter
  settings, highwater marking, file extension processing, I/O (read
  and/or write) caching, available physical memory, I/O caching
  settings, and any number of other areas.  Application profiling
  is often required, and the assistance of OpenVMS Engineering and
  particularly the assistance of the softwarae vendor can be central
  in an expeditious resolution.

answer written or last revised on ( 22-MAY-2001 )

» close window