difference between OverFlow ans Extended Storage Group



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difference between OverFlow ans Extended Storage Group

Postby samb01 » Mon Dec 17, 2018 6:48 pm

Hello,
but i read the doc ibm:

https://www.ibm.com/support/knowledgece ... lsgval.htm

but i can't anderstand the diference between Extended SG and Overflow SG

Is an Extended SG must be en Overflow SG ?

If i declar an Extended SG, it is usefull to define it in ACS Routine ?

Thank's for your help, it's because i'm not sure of my english.
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Re: difference between OverFlow ans Extended Storage Group

 

Re: difference between OverFlow ans Extended Storage Group

Postby Robert Sample » Mon Dec 17, 2018 7:31 pm

Is an Extended SG must be en Overflow SG ?
The site you quoted tells you:
An overflow storage group may also be specified as an extend storage group.
An extend storage group may also be specified as an overflow storage group.
So either may exist without the other, or either can be defined as the other -- your choice. The site also tells you the difference between the two.
Overflow:
If all volumes in a non-overflow storage group are so full that the current allocation request will push them over high threshold, while volumes in the overflow storage group are not so full, then the new data set will be allocated on a volume in the overflow storage group. The assumption is that all other attributes of the non-overflow storage group and overflow storage group and the volumes in those storage groups are the same.
Extended:
Specifies the name of another pool storage group to which data sets from the primary storage group can be extended when there is an insufficient amount of storage on the primary storage group. A primary storage group is the storage group in which the initial allocation resides.
In other words, if a CURRENT ALLOCATION will push the storage group over the high threshold, overflow will be used instead. Extended doesn't look at the current allocation, but rather at the current data sets which need additional extents.
If i declar an Extended SG, it is usefull to define it in ACS Routine ?
Whether or not it is useful will depend upon what you're doing -- if you want the extended SG to be used for initial allocations, then you MUST include it in the ACS routine. If you don't want to use it for initial allocations, then you don't need to include it.
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Re: difference between OverFlow ans Extended Storage Group

Postby samb01 » Mon Dec 17, 2018 9:29 pm

Thank you Robert Sample for your help, i would like to be sure of that because my english is not very good :oops:

My problem is E37 in my Storage Group occurs.

So I'd like to create an Extended Storage Group to allow the dataset allocate in the other Storage Group. So i don't have to declare it n the ACS Routine.

This is my eror :


IEC032I E37-04,IFG0554P,XSAVE10,S10,VCFP,266C,XDU243,  313  
DATASET.G0010V00                                              

 
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Re: difference between OverFlow ans Extended Storage Group

Postby Robert Sample » Mon Dec 17, 2018 9:43 pm

Adding an Extended Storage Group may not resolve your E37 ABEND. From the Messages and Codes manual on the IEC032I message:
04
A data set opened for output used all space available to or on the current volume, and no more volumes were available. Change the JCL to specify more volumes.

Not enough volumes were specified for the data set, through the SER, volume count, or REF subparameter of the VOLUME parameter of the DD statement. When all the volumes were filled, the program attempted to write another record.
For a partitioned data set on a direct access volume or for a VIO data set, all space was filled when the program attempted to write another record. (A partitioned data set or a VIO data set can reside on only one volume with a maximum of 65535 tracks.)
For a partitioned data set on a direct access volume, 16 extents had been used when the program attempted to write another record.
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Re: difference between OverFlow ans Extended Storage Group

Postby samb01 » Mon Dec 17, 2018 11:24 pm

Yes but i've already coded VOL=(,,,59) and the error je E37-04.
Si by addict an extended sg, the system Will allocate other volumes into the extended SG.
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Re: difference between OverFlow ans Extended Storage Group

Postby Robert Sample » Mon Dec 17, 2018 11:33 pm

If your data set is already on 59 volumes, it will not matter if you add an Extended Storage Group -- the limit is 59 volumes, no matter how many storage groups you specify.
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Re: difference between OverFlow ans Extended Storage Group

Postby samb01 » Tue Dec 18, 2018 12:24 am

I thought it will choose a volume available in the extended storage group instead of choosing à volume with no space in the primary storage group.
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Re: difference between OverFlow ans Extended Storage Group

Postby Robert Sample » Tue Dec 18, 2018 12:52 am

From the MVS JCL Reference manual (V2R3) page 311:
DASD volumes cannot be removed from the drive. Therefore, the number of volumes for a data set is the same as the number of drives for the data set. This number cannot exceed 59.
For a tape data set the number of volumes can be more or less than the number of drives. The number of drives cannot exceed 59. The number of volumes cannot exceed 255
In other words, if you have a data set that has allocated 59 volumes in the storage group(s), it doesn't matter if you use Overflow or Extended Storage Groups -- you're not going to get any more allocations, period. I think you're mixing up two concepts -- IF the primary storage group has not enough space on any volume, AND there are less than 59 volumes allocated to the data set, the system will choose a volume in the extended storage group. If the (disk) data set has 59 volumes allocated, then it will not -- under any circumstances -- go to a 60th volume. For tapes, the limit is extended to 255 volumes but tapes are not disk and disks are not tape.
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Re: difference between OverFlow ans Extended Storage Group

Postby samb01 » Tue Dec 18, 2018 1:35 am

Robert, i anderstood the dataset cannot exceed more than 59 volumes. But as my dataset je an extended format, stripped with compaction the system will ( for example) choose 30 volumes available in primary storage group and 29 volumes available in the extended storage group.
Or if this solution doesn't work, May be the solution je using multi stired storage group.
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Re: difference between OverFlow ans Extended Storage Group

Postby Robert Sample » Tue Dec 18, 2018 1:54 am

The question has been asked -- and answered. You're not going to get better answers by asking over and over. At this point, TRY IT AND SEE WHAT HAPPENS! Eventually you have to either go with extended storage groups or give up on the concept.

Topic locked to prevent further waste of time.
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