Data set extent question

MadHadder · New User Joined: 09 Apr 2008 Posts: 9 Location: Virginia

Good morning all, I'm puzzled with something. I have a DB2 data set that keeps taking extents that are very small in size, I'm curious if the reason it is taking these extents could be due to very fragmented volumes in the pool of DASD that our DB2 files use? Would fragmented volumes cause the file to continue to take extents even if they are very small extent sizes? I'm trying to avoid hitting the max extents for this file.

Thanks

dick scherrer · Posted: Wed May 09, 2012 9:49 pm

Hello,

Suggest you work with your storage management people to find space to re-allocate this data set down to a single (or few) extents.

vasanthz · Posted: Wed May 09, 2012 10:30 pm

Will it work if we force migrate the dataset using HMIG and then HRECALL the dataset immediately, so it will be in single extent or few extent?

dick scherrer · Posted: Wed May 09, 2012 11:47 pm

Hello,

Suggest this only be done after DB2 has been shut down. . .

Pete Wilson · Posted: Tue May 15, 2012 9:32 pm

You need to check whether the DBA's have settings defined to create small secondary extents. What is the primary extent like? You could ask them about 'Sliding Secondaries' which causes DB2 to allocate increasingly large secondaries as it extends but I think that is a blanket setting.

One thing you can do is get the file deallocated and run a DFDSS COPY to move it and it will try and allocate it in one large primary extent.

It could be due to fragmentation as well but if that was the case each extent is likely to be a different size.