RE: VSAM file allocation on multiple disks

[MARK BOLTAX]

Frank,

As a side thought...

If you do not want any secondary allocations on any of the volumes you use just define the secondary allocation larger than the space available on any volume. You may want this to spread the space evenly across all the volumes or to prevent running out of extents by filling each volume with many secondary extents. 

You can also do this by making the primary allocation large enough to use all of the space on each volume.

Mark Boltax 917-648-6029

On Wed, Sep 16, 2015 at 02:21 PM, Frank M. Ramaekers wrote:

THANKS!   That’s what I thought.

 

Frank M. Ramaekers Jr.

 

From: VSE-L [mailto:vse-l-bounces+framaekers=ailif...@lists.lehigh.edu] On Behalf Of Duerbusch, Tom
Sent: Wednesday, September 16, 2015 1:13 PM
To: VSE Discussion List
Subject: Re: VSAM file allocation on multiple disks

 

The first disk gets the primary allocation (in up to 5 extents if necessary), the the first disk gets secondary allocations (up to 16 minus the number of primary extents for a reuse file), then it is repeated for each of the secondary packs in order that they are specified in the DEFINE CLUSTER.

If you don't have sufficient space on a pack for the primary allocation, that pack is skipped and another attempt is made on the next pack.

 

If you are using MODELs, such as I have for VSE VTAPE, in the model definition, you specify all the volumes you want to be able to use (in one of my shops that is 176 model 9 volumes), and don't specify the VOLUME parm in the DEFINE CLUSTER.  VSAM will pick 16 candidate volumes from the model.  (It doesn't look random but it does spread the usage out.)  As a reuse cluster can have up to 123 extents, 16 candidate volumes with 16 extents each (256 total) allows the 123 extents to be allocated when some of the volumes are full or near full.

 

Tom Duerbusch

THD Consulting

 

On Wed, Sep 16, 2015 at 12:58 PM, Frank M. Ramaekers <FRama...@ailife.com> wrote:

I need to define a file that spans multiple disk and want to understand how file space will be allocated.  I know that primary space is allocated first on each volume, but when does the secondary space come into play.  (Does the disk first allocated the a primary then as many secondarys that will fit then the 2^nd disk has a primary allocated or does all primaries get allocated first?)

 

Frank M. Ramaekers Jr. | Systems Programmer | Information Technology | American Income Life Insurance | 254-761-6649

 

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