Colin Allinson wrote:
We run 6 LPARS on a busy 6 way 2084 and have a VERY large number of
devices (mostly DASD).
IPL times can be very long ( 90 minutes, or more, for low priority
LPAR at busy times).
My initial reaction was that this is caused by the time taken to sense
devices and build the device blocks. The length of time a system will
hang, (more than a minute for 256 devices), when building a range of
device blocks when they are dynamically defined seems to support this.
I have been trying to tune this using devices NOTACCEPT/ACCEPT list in
the SYSTEM CONFIG to eliminate unnecessary devices but the results
have been inconsistent and a little confusing.
Last night I tried multiple IPL's on a small system in a medium/low
priority LPAR. Before any tuning this IPL'd 2 weeks ago in 30 minutes
in the relatively low load evening period I was using for my tests.
For these tests I had set :-
- Devices Notaccept 0000-FFFF
- Devices Accept nnnn-nnnn Multiple specific ranges
- Devices Notsensed 0000-FFFF
- Devices Sensed nnnn-nnnn Same multiple ranges
as above
- Devices Online_at_IPL 0000-FFFF
- SET RDEV for each range.
There are just over 12000 recognised devices (mostly DASD)
During the tests I was watching the System Activity Display on the
HMC. Throughout the test the overall cpu activity was between 60-80%
and there was no excessive channel activity shown. However, the system
being IPL'd did use huge amount of processor resources (up to 360% of
its allocated share).
In the first test the IPL completed in 6 minutes - great result but
some of my SET RDEV statements were in error and ignored.
Second IPL with these corrected took 26mins 35secs
Third IPL with the RDEV statements (that were originally ignored)
removed took 31 mins 45 sec.
Later on a larger system with many more devices and no tuning in the
system config IPL'd in 20 minutes.
My questions are :-
- Am I just fooling myself that restricting the device range
will help (i.e. the 6 mins was anomalous)?
- Is the time taken to sense a device the same if it exists or
not?
- Are there any other suggestions of things I can do to speed
up IPL time?
Any advice would be much appreciated.
Colin Allinson
Amadeus Data Processing
There was a thread about this problem not too long ago. We have a large
number of dasd devices, too and do not have your problem. The 6 minute
figure is about normal for us. A good deal of that time is during
initialization after the ipl - spool (we have several thousand files in
spool at any given time), SFS and VTAM are major offenders. I have
configured many devices that are z/OS only Offline_at_ipl, but none are
ignored. I have specified 0000-FFFF as sensed and a large number of
Offline_at_ipl ranges. There are many more offline than are online, but
all are sensed.
What you are describing as hangs could be the system waiting for channel
time-out caused by improperly terminated channels. I don't know the
timeout interval for the newer systems, but it used to be 7 seconds per
device. The timeout would only occur for devices that are not present on
a channel. If you check the prior thread, there are other suggestions.
Probably you will find the answer there.
