ADSM-L

Re: VM or MVS Server: Which Way to Go

1993-11-11 16:07:24
Subject: Re: VM or MVS Server: Which Way to Go
From: Jeff Savit <TXJEFF AT VMETH3.OSSD.GIS.ML DOT COM>
Date: Thu, 11 Nov 1993 16:07:24 EST
>The MVS server has slightly better performance than the VM server due to some
>better Disk IO capabilities on MVS than on VM (10% - 20% better performance on
>disk related activities).  Other than that, the reasons to decide are based
>on network bandwidth to the processor, capacity (disk/tape/CPU) of the
>processor, and the comfort level of support personnel to run it.
>
>
>Paul Bradshaw
>
>>Paul 10%-20% seems to be a big difference in performance unless there is
>>something other than Disk IO capabilites that affects performance.
>> Leonard Boyle

I think this is one of those almost unanswerable questions, since the
results can be altered by so many factors.  I don't know of any particular
reason to believe that MVS outperforms VM for I/O; in fact, I just came out
of a meeting where one of the points raised was VM's ability to sustain a
very high SIO or SSCH rate compared to MVS.  Certainly, when adding the
different possibilities for minidisk cache and disk placement, there are
lots of different possible resuls.  Generally, MVS has a much higher storage
requirement (so VM will outperform it in storage constrained enviromnents),
and a higher cost for switching between address spaces than VM does for
switching between users - which is significant when moving back and forth
between TCP/IP and ADSM.  VM makes very good use of multiprocessors, so there's
no disadvantage for VM there. I don't know how ADSM exploits multiprocessors.
Aren't there several worker machines doing actual transfers?  That would help
exploit multiprocessors.

I think the total issue of which system is "best" for ADSM is much more
complicated (I think we probably all agree on this).  I personally prefer
VM for this, believing it to be the more natural fit with TCP/IP and other
client-server technologies.
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