about space

ksivapradeep · Active User Joined: 30 Jul 2004 Posts: 101

in mainframes refresher material one concept is like this,

he has given space=(trk(20,20),RLSE),he told that in worst case the system wil allocate 80 tracks how its 80 please explain me.

regards,
siva pradeep

mmwife · Super Moderator Joined: 30 May 2003 Posts: 1470

Hi Siva,

The space allocation you showed specifies a request for 20 trks primary and UP TO 15 additional 20 trk extents when the primary alloc has been exhausted.

I emphasized the UP TO because up to 5 extents can be used to satisfy the primary alloc. If 5 extents ARE used, then only 10 extents at maximum can be used for secondary allocations. Doing the math, the worst case alloc is 220 trks, not 80. By my reconing, anway.

As a side note, it's interesting that this same dataset when allocated to 5 volumes can contain a max of 1520 trks.

lramani · Posted: Tue Nov 09, 2004 10:10 am Post subject:

Hi,

Wanted a small clarification on how u came to 220 trks in the worst case.

If the primary is 20 trks and the secondary is 20 too...then its 20 + 15*20 = 320 trks. (this i was aware of)

As per your second statement ...to be very honest which I was unware of states that
If 5 extents ARE used, then only 10 extents at maximum can be used for secondary allocations.
which means 5*20 + 10*20 = 300 trks.

So, can u please explain how did 220 trks in the worst case come in.

sorry, if i made some mistake in understanding what you actually meant.

mmwife · Super Moderator Joined: 30 May 2003 Posts: 1470

Hi lramani,

If the primary space requested is available in one contiguous area only 1 extent is used to allocate it. If contig space is NOT available on the volume, up to five extent are used to satsfy the primary space request. These extents are subtacted from the 16 total extents available to the volume. Those extents remaining are used to satisfy the secondary space requested (in this case 11 extents, not 10 as I originally stated).

So, it can take 5 extents to alloc the primary req. These 5 extents are subtracted from the orig 16, and secondary space availablr to the dataset is 11X20 =220 + 20 primary = 240. Since I used 10 2ndary extents I erroneously calculated 220.

In the multi-vol allocation example I posed it gets even more confusing. If the 2ndary space is not available on a given volume, that vol is skipped, so its possible to allocate only 1 extent of 3 trks on one vol, 1 extent of 7 trks on another, 16 extents of 20 trks each on the next, 0 trks on the next, etc.

It all depends on the space available on each vol. If there are no vols remaining to allocate the extent or there are no remaining extents for the dataset, an X37 abend results.

ksivapradeep · Active User Joined: 30 Jul 2004 Posts: 101

hi jack,

is there any specific limit that the pimary will take 5 extents first then the remaining is 11.in mainframes refresher book i have seen that in worst case it will give 80 trks how he calculated that one.and another thing is max how much space aloocates for that particular space parameter.

thanks for reply,

regards,
siva pradeep

ksivapradeep · Active User Joined: 30 Jul 2004 Posts: 101

hi jack,

is there any specific limit that the pimary will take 5 extents first then the remaining is 11.in mainframes refresher book i have seen that in worst case it will give 80 trks how he calculated that one.and another thing is max how much space aloocates for that particular space parameter.

thanks for reply,

regards,
siva pradeep

mmwife · Super Moderator Joined: 30 May 2003 Posts: 1470

Hi Siva,

Sorry, I can't explain how "he" came to 80 trks. I'd have to see his explaination of his thesis. I can give you some "facts" on the subject:

Primary space is allocated by attempting to satisfy the request in 1 contiguous extent. In this case 20 trks. If there isn't enough contig space to satisfy it, the next largest contig space is used (for ex. 12 trks). The remainder of the alloc is sought as contig space. If THAT is satisfied, the primay space req was satisfied in 2 extents (12 and 8 trks). If not the alloc process continues until either the primary req is satisfied in 5 extents or less or an x37 abend is generated.

In the ex. above, if the primary space req was satisfied in 2 extents, the 2ndary extents are limited to 14 and a max space of 300 trks. If satisfied in 1 extent then 2ndary extents can number 15 for a max space of 320 trks for the dataset.

Keep in mind that the 2ndary space numbers represt max trks alloc for an extent, not ACTUAL. At any time the number of contig trks req for 2ndary alloc may NOT be available on the vol. But if there is at least ONE trk avail, it will be alloc to that extent. As the pgm continues to execute (and uses space previously alloc) more space may become available on the vol, so the NEXT extent May get the full 20 trks (or maybe something less). But if, at any time the allocation cannot acquire ANY space, an x37 abend results.

This is probably more than you wanted to know

and we didn't even cover SMS! You're lucky; I don't know much about SMS.