Joined: 26 Nov 2002 Posts: 12375 Topics: 75 Location: San Jose
Posted: Tue Feb 11, 2003 9:43 pm Post subject:
Naveen,
Space is allocated for non-system-managed data sets or system-managed data sets without the guaranteed space attribute in the storage class in the following way. Suppose you allocate a new data set and specify SPACE=(TRK,(2,4)); this initially allocates two tracks for the data set. As records are written to the data set and these two tracks are used up, the system automatically obtains four more tracks. When these four tracks are used, another four tracks are obtained. The same sequence is followed until the extent limit for the type of data set is reached.
A physical sequential data set can have 16 extents on each volume.
An extended format sequential data set can have 123 extents per volume.
A partitioned data set can have 16 extents.
A direct data set can have 16 extents on each volume.
A VSAM data set can have 255 extents.
A PDSE can have 255 extents.
Allocate space for a multivolume data set the same way as for a single volume data set. DASD space is initially allocated on the first volume only (an exception is extended format data sets). When the primary allocation of space is filled, space is allocated in secondary storage amounts (if specified). The extents can be allocated on other volumes.
Multivolume VSAM Data Sets: When a multivolume VSAM data set extends to the next volume, the initial space allocated on that volume is the primary amount. After the primary amount of space is used up, space is allocated in secondary amounts. By using the DATACLASS parameter, it is possible to indicate whether to take a primary or secondary amount when VSAM extends to a new volume.
Multivolume Non-VSAM, Non-Extended Format Data Sets: When a multivolume non-VSAM (non-extended format) data set extends to the next volume, the initial space allocated on that volume is the secondary amount.
Striped Extended Format Data Sets: When space for a striped extended format data set is allocated, the system divides the primary amount among the volumes. If it does not divide evenly, the system rounds the amount up. For extended format data sets, when the primary space on any volume is filled, the system allocates space on that volume. The amount is the secondary amount divided by the number of stripes. If the secondary amount cannot be divided evenly, the system rounds the amount up.
Extended format data sets have a maximum of 123 extents on each volume. (Physical sequential data sets have a maximum of 16 extents on each volume.
Extended format data sets, have the same characteristics as physical sequential data sets. Records are not necessarily stored in the same format or order as they appear. An extended format data set can be referred to as a striped data set if its data are interleaved across multiple volumes. This is called "sequential data striping."
Extended format data sets can be allocated only on SMS-managed volumes. An extended format data set will not be allocated in a storage group containing mixed device types.
A PDSE can have up to 255 extents. Since a PDSE can have more secondary extents, you can get the same total space allocation with a smaller secondary allocation. A PDS requires a secondary extent about eight times larger than a PDSE to have the same total allocation. Conversely, for a given secondary extent value, PDSEs can grow about eight times larger before needing to be condensed. Defragmenting is the process by which multiple small extents are consolidated into fewer large extents. This operation can be performed directly from the ISMF data set list.
Check this link for a detailed explanation of differences between PDS and PDSE
Joined: 01 Dec 2002 Posts: 28 Topics: 8 Location: India
Posted: Sat Feb 22, 2003 4:53 am Post subject:
Hi ,
I created the seq dataset(PDS) with SPACE=(TRK,(2,4),2) is it possible to increase in future when all the space is used. By the by is there that a dataset created with the SPACE=(TRK,(2,4),3) can have only a specified number of PS.
That is it possible to increase the Directory Blocks.
Joined: 03 Jan 2003 Posts: 1014 Topics: 13 Location: Atlantis
Posted: Sat Feb 22, 2003 1:13 pm Post subject:
You can modify the size of secondary extents by respecifying it in the JCL allocation for some job that opens the data set (the vtoc is updated when the data set is closed), but that will not affect existing extents, so if the data set is already full, then you are out of space.
At this point, you can either copy the data to a new data set, or sometimes migrating and recalling the data set will consolidate extents to give you more room for expansion.
As for directory size increases, there are some programs (non-IBM) that do that. Probably PDS, FileAid, StarTools, etc. But the recommendation from IBM is to use PDSE instead of PDS. That has no predetermined directory size so the number of members is limited only by the total size of the data set.
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