  I/O Performance on VAX via DSSI? 
 The Question is:
 
Question relates to writing information to disk in a high volume, high
 reliability scheme.
Is it possible to set up shadowing with the following?
1. 4MBlock DECram (8 Ram Disks, 500000 blocks each)
2. a partition on a 9 gb hard disk (HSD10 or HSD30 array)
3. a partition on a 9 gb hard disk
 
HSDxx controllers would be connected to two DSSI channels from separate KFMSA
 cards in a fail-over mode,
 
Ram Disk would provide for extremely high output rate, shadowed drives would
 provide reliability.
 
I am afraid this question will stimulate even more questions - maybe we could
 correspond via email...
Jim
 
 The Answer is :
 
  A requirement for high-performance I/O, the use of the DSSI bus (roughly
  equivilent to SCSI-1 in performance), the use of OpenVMS VAX V6.2, and
  the use of an unspecified-model XMI-based VAX system makes for a rather
  interesting configuration, and would not comprise a configuration that
  the OpenVMS Wizard would initially consider for the stated task.
 
  You can shadow dissimilar devices, assuming the total numbers of blocks
  match and assuming you have current OpenVMS versions and current shadowing
  ECOs installed.
 
  Shadowing will not assist your performance goals here, as shadowing will
  require writing to all three spindles involved in the shadowset, and you
  have a DSSI bus in the way.  Shadowing can potentially assist with read
  performance, and particularly if you have a fast storage device available
  in the shadowset.  Shadowing will not assist with write performance, and
  particularly not if you have a slow storage device configured into the
  shadoset.
 
  Most any AlphaStation or small AlphaServer system configuration will
  greatly exceed the I/O performance of this VAX and DSSI configuration,
  as it will permit the use of Fibre Channel and/or UltraSCSI or faster
  storage.
 
  The OpenVMS Wizard is not in a position to provide consulting services,
  nor to provide email services.
 
 Answer written or last revised on  18-OCT-2001 
