CSYSMAS@UCLAMVS.BITNET (Michael Stein) (07/08/89)
All these questions are about CP's DASD Block I/O System Service.
1. Can multiple Virtual Machines use this service in multi-write
mode on the same disk at the same time? I am assuming that
these VM's are responsible for the interlocking, I just want
CP to get the I/O done. (It's not a CMS format disk).
2. Can I use the whole disk (offset = 0)?
3. Can I use negative block numbers if the offset isn't zero?
4. How do I initially format the mini-disk? (CKD/FBA)?
(This doesn't have to be fancy. Filling it with 4k blocks
would be fine as long as all the blocks are there).
5. Is there a non-standard length block near the begining of
the mini-disk (like a volume label at record 3?)CSYSMAS@UCLAMVS.BITNET (Michael Stein) (07/13/89)
As an MVS person, I always thought this was a VM list, but
since I haven't received even one response so far I've decided
it's just a CMS list... Anyone have any information on this?
(last chance on this list).
- - -
All these questions are about CP's DASD Block I/O System Service.
1. Can multiple Virtual Machines use this service in multi-write
mode on the same disk at the same time? I am assuming that
these VM's are responsible for the interlocking, I just want
CP to get the I/O done. (It's not a CMS format disk).
2. Can I use the whole disk (offset = 0)?
3. Can I use negative block numbers if the offset isn't zero?
4. How do I initially format the mini-disk? (CKD/FBA)?
(This doesn't have to be fancy. Filling it with 4k blocks
would be fine as long as all the blocks are there).
5. Is there a non-standard length block near the begining of
the mini-disk (like a volume label at record 3?)RKOGUT@BROWNVM.BITNET ("R. Kogut") (07/13/89)
It's been years since I looked at this, so there may be errors here, but as you're not getting a lot of response... *BLKIO works on normal VM minidisks; R/O or R/W access is controlled by the CP directory and/or link command. Any locking protocols must be supplied by the users. The easiest way of formatting the mdisks is with CMS FORMAT -- you have a choice of 512, 1024, 2048, or 4096 byte blocks. I can't remember, but I think the label is in whatever block size you choose, not 80 bytes. In any case, the relative record order should be respected. You can't use negative offsets. *BLKIO was designed to allow SQL to run with some semblance of performance. Normally, after the disk is formatted, the RESERVE command is used to create a single mode 6 file which contains all of the blocks not used for labels or CMS file directory. The HELP file for the RESERVE command contains a good descrip- tion of the layout of the physical blocks.
TIMMO@JHUHYG.BITNET (Tim DiLauro) (07/13/89)
On Wed, 12 Jul 89 12:59:00 PDT Michael Stein said: > As an MVS person, I always thought this was a VM list, but > since I haven't received even one response so far I've decided > it's just a CMS list... Anyone have any information on this? > (last chance on this list). > No need to be nasty. People usually wait a little bit to see if someone more (read truely) knowledgable responds to the mail first. > - - - > >All these questions are about CP's DASD Block I/O System Service. > >1. Can multiple Virtual Machines use this service in multi-write > mode on the same disk at the same time? I am assuming that > these VM's are responsible for the interlocking, I just want > CP to get the I/O done. (It's not a CMS format disk). Access to these minidisks is controlled by CP, so the MW access mode of the CP LINK command should allow you to do that with little trouble. > >2. Can I use the whole disk (offset = 0)? You can use the entire area of the file created by the CMS RESERVE command (discussed under item 4.). The volume label and other system areas on the minidisk (IPL blocks, allocation blocks, pointer blocks) will not be available through the *BLOCKIO system service. > >3. Can I use negative block numbers if the offset isn't zero? no. > >4. How do I initially format the mini-disk? (CKD/FBA)? > (This doesn't have to be fancy. Filling it with 4k blocks > would be fine as long as all the blocks are there). The initial format of the disk is done with the standard CMS FORMAT command. You can specify and of the normal EDF blocksizes (512, 1K, 2K, 4K). You cannot use the old CDF compatibility blksize of 800. A file with mode 6 is created in the usable area of the minidisk by the CMS RESERVE command. It is the RESERVE command that does not support a blksize of 800. > >5. Is there a non-standard length block near the begining of > the mini-disk (like a volume label at record 3?) Keep in mind that this is a CMS minidisk. It just has one file on it. Like any other CMS minidisk it has the volume (CMS1) record at block or physical record 3. The length of that record will be the blksize that was used (explicitly or by default) in the FORMAT command. One more thing: The *BLOCKIO system service is an IUCV connected service. Each disk you are using *BLOCKIO with requires an IUCV connection. If you are communicating with another VM via IUCV then that will also take up an IUCV path. By default there are only four such paths per VM. If you plan to have more then you will need to code an "OPTION MAXCONN ????" in the directory entry of each VM requiring more than four paths. Smooth sailing! Tim DiLauro (301)955-4770 Systems Programmer Johns Hopkins University School of Hygiene and Public Health