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VSAM's DATACLASS attribute

 
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quanzhong

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Joined: 12 Aug 2008
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Location: china

PostPosted: Fri Sep 19, 2008 8:43 am    Post subject: VSAM's DATACLASS attribute
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Hi,
can anybody tell me the advantage of defining various DATACLASS? and how it affecs performance? thanks...
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dick scherrer

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Joined: 23 Nov 2006
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PostPosted: Fri Sep 19, 2008 8:57 am    Post subject:
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Hello,

Your best source of info will be your storage management people. They can tell you how/why your system has been defined as it is.

The advantage of using these is in managing the resources.
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expat

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PostPosted: Fri Sep 19, 2008 11:19 am    Post subject:
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The DATACLAS is used to allocate datasets with a number of physical attributes, and is required when extended addressability is used.

If any GDS has a valid DATACLAS assigned, be it DASD, Tape, SMS or non-SMS then there is no need for a model or dummy dscb to be coded.

In reality the DATACLAS is not really an important part of the SMS scheme of life - well that is the view of me, as a storage guy.
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Anuj Dhawan

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PostPosted: Fri Sep 19, 2008 2:31 pm    Post subject:
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Hi,

DATACLAS (imho) is used primarily by storage management to classify and manage the dasd resource of the organization. This includes allocating the appropriate dasd by data/business classification, defining the migration strategy for datasets by rule to ensure space availabbility, and is often an integral part of the overall backup strategy.

For more info, you can check this link

http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/IEA2B650/12.15?DT=20040712170508


PS. Your subject line actually makes me feel that you wanted to ask something else.. icon_confused.gif
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expat

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PostPosted: Fri Sep 19, 2008 2:48 pm    Post subject:
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Anuj,

Just for your clarification, the space availability (migration and backup strategy) is defined in MGMTCLAS and the allocation of specific DASD is by STORGRP.

STORCLAS can be used to further breakdown the allocation to different DASD types within a pool - although this is more rare these days with high speed DASD and DASD fast write and various other hardware capabilities.
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Anuj Dhawan

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PostPosted: Sat Sep 20, 2008 2:26 am    Post subject:
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Thanks Expat, your explanation are always (usually) are bookmarks entry for me... icon_smile.gif
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quanzhong

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PostPosted: Sat Sep 20, 2008 3:12 am    Post subject:
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Hi, Anuj
Quote:

PS. Your subject line actually makes me feel that you wanted to ask something else.. icon_confused.gif

actually, now i plan to define 10 Vsam file(file0-file9) with the same attribute for file segmentation.. but at present, we just use fileA, and the rest 9 files are empty..as file1 can be very large, so we have assgin DATACLASS(VSLRG)( in our shop, there are VSSML, VSMED,VSLRG dataclass, mainly to limit the file size,VSLRG for file > 4G bytes).. but now I want to assign DATACLASS(VSLRG) to other 9 files, though they may be remain empty for a long time, possiblely more than 1 year..

so my doubt is, if i do that, what the disvantage would be?
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expat

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PostPosted: Sat Sep 20, 2008 2:47 pm    Post subject:
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Have you considered using VSAM data striping for your very large file.

This was developed for exactly the situation of a very large VSAM dataset and is usually good for performance with large sizes.

Have a chat with your storage people and see what they can do for you.
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