PAV use in zVSE
Victor, C. T. Hsiao
I recently installed a zVSE V5.2 using IBm DS8884 which supports PAV. All the setup is O.K. I have 3 alias addresses for my DOSRES and SYSWK1. After turning on the SMF, I noticed that the IO count for one alias is much larger than the IO count for the base address, and the other two alias has near-zero IO count.
I read from document that "z/VSE does load levelling for parallel I/O’s by selecting a “free” device among the available base and alias devices." But it looks like that z/VSE tends to select the alias instead of the base. Another possible reason is that the device(base or alias) selection was made during task startup, not for every I/O.
I also read from the same document that "Subsystem Monitoring Facility (SMF) is enabled to collect base device information only". Therefore maybe this is the third possible explanation.
Is there anyone have the same experience?
michael...@gmail.com
I think the bit about "collecting base device information only" may be related to having one set of I/O timings (QUEUED etc.) and not one set for the base and one per alias, but I could be wrong.
Mike
Ken and Mary Meyer
I would not recommend using it in production if you have any products
(BIM/CSI or CA former GOAL products, for example) or other third
party vendors that use special means to protect file/member integrity
within and between individual z/VSE and z/VM instances without using
the lock mechanisms available for those operating systems.
Ken
snip..
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Mick Poil
That sounds rather worrying. What kind of fallout can there be? I don't remember anything like this being mentioned before.
Mike
Ken and Mary Meyer
function properly. I mentioned this to VM people at multiple WAVV
conferences, as well as reporting it as an issue. There is a way to keep
them treated as a single "operation", but it was not working properly. My
research is property of CSI and CA now, so I do not have access to it.
If you want more "proprietary" information, email me privately.
Avihu Gershoni
I read with interest the posts about PAV because I am considering using it at my next storage replacement.
I read the white paper and the section in the Administration manual, but did not find a clear answer to the question:
Should PAV-alias devices be considered in counting the total number of devices defined by the IODEV parameter?
The manual does specify that you must define only base addresses in the IPL and can use only 1023 devices out of the 1024 defined by IODEV in a system with PAV because PAV activation requires to have one ‘spare’ I/O device eligible, but is the spare I/O device the only address "lost" by using PAV?
Avihu Gershoni
Mainframe System Department Manager
Hilan Limited
8 Meitav Street
Tel Aviv
Israel
Mick Poil
Avihu Gershoni
Hello Mick,
I used your advice and this is the answer I got from Natalie Speiser from IBM Systems & Technology Group, Systems Software Development:
" The actual number of devices is calculated during IPL through the corresponding ADD statements. Since you only add the PAV base devices, PAV alias devices are not considered.
In z/VSE we allocate one dummy device for PAV initialization - no matter how many base devices have been added. So if you define 1024 devices, you can actually use only 1023."
Avihu
Ernie J. Carney
1023 devices would be more than enough if z/VSE was allowed to use the huge DASD devices that z/VM and z/OS are allowed. z/VSE currently has a max disk size of 65520 Cylinders. z/OS and z/VM max is closer to 256,000 cylinders. I placed an RFE on IBM’s web Site last year and have heard nothing.
E J Carney
CTO
DOB Systems, LLC
Kevin Corkery
Sounds like a use for an FOR in your CICS environment.
From: VSE-L [mailto:vse-l-bounces+kcorkery=live...@lists.lehigh.edu]
On Behalf Of Avihu Gershoni
Sent: Monday, August 29, 2016 11:55 PM
To: Vse-L (vs...@Lehigh.EDU)
Cc: Ernie J. Carney
Subject: RE: PAV use in zVSE
Ernie,
I could live with the 1024 devices limitation defined by IODEV if all my disk devices were defined as 3390-54 for the foreseeable future, but the real limitation is not this but the 255 logical units per partition. This limitation can prevents opening a VSAM file in CICS if it needs new logical units beyond the maximum of 255.
Avihu
Mick Poil
Lou Winston
If function shipping is so expensive, what about the VSAM redirector and all that stuff? How expensive is that?
L.W.
Sent: Wednesday, August 31, 2016 5:49 AM
To: VSE Discussion List
Subject: Re: PAV use in zVSE
Mick Poil
Lou Winston
Actually it sounds like they are good candidates for conversion to z/OS
Sent: Tuesday, August 30, 2016 9:34 AM
To: 'VSE Discussion List'