Re: Journal ASPs

Gordon Searles wrote:
> 
> We have 4 AS/400s with 30 - 120 GB of RAIDed DASD on each.  2 of the 4
> systems have journal ASPs.  Ideally we would like to have all 4 systems
> the same.  IBM used to recommend a seperate user ASP for journalling
> for     performance and protection.  Now with RAID they seem to be saying
> that the benefits are no longer there, is that true?  What is your
> experience?  Do you have a seperate user ASP for journalling?  Are you
> going away from or towards journal ASPs?  Is this a decision that you
> can make for all of your systems or do you decide
> system by system?  What do you use as your criteria for creating a
> journal ASP?
> 
> Thanks,
> --
> Gordon Searles
Gordon,

   I prefer a separate ASP for the Journal Receivers. The journals
themselves must reside in the same ASP as the file that it is being
journaled.  Think of writing to the journal receivers as a sequential
tape.  Each time you write a record you only have to move the tape a
little further, this is much better than writing to a tape randomly (ha
ha, if only possible).  Well expand on that, to get better performance
we block the writes. Now lets move that analogy to receivers & DASD.  On
your ASP with the journal receivers, you have a set of arms that are
ready to write the next block to disk, the arms are already in place. 
If your receiver was "scattered" across all your disks, you would be
contending with other writes and your arms would not be in position to
write the next journal entry to the receiver.  By putting the Journal
receivers to their own ASP, the disk arms are always ready to write, and
best of all they don't have to move.  Moving of the disk arm is the
slowest function of the disk.  

   That is the reason I use a separate ASP.

   HTH

   Pete Massiello
   OS Solutions
   Voice (203)744-7854 Ext. 11
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