calculating transfer size on vms disk

[mark_511]

how can I calculate the transfer size on a vms disk. Required for setting chunksize on RAID set. I need to find what the average transfer size is to the current drive.

[Ian Miller.]

on current version of VMS see
SHOW MEM/CACHE/FULL

[mark_511]

Yes, tried this first but lists x Block IO. What does "Block IO" refer to in this context

[labadie_1]

Until recently, most of the I/O made were of less than 16K.

$ monitor disk/item=all

gives the queue length and the I/O operation rate. If you find how many I/O your model of disk gives when it has a queue length of 1 (for example), then it will be quite easy.
Check the specs of your disk.

[Wim Van den Wyngaert]

Performace advisor can give you the IO size per program.

Wim

[mark_511]

no, sho cache gives me what I need but I require clarification of what the "Block IO" refers to. Is it Bytes, Blocks (if so what size), K?

[Wim Van den Wyngaert]

Current setting of the system parameter
VCC_MAX_IO_SIZE in blocks.
The extended file cache (XFC) will only cache files up to this size.

So it is blocks and for all IO's bigger than 127 blocks there are no statistics.

Wim

[Wim Van den Wyngaert]

And show mem is not per disk.

PA can give you the IO size per disk.

Wim

[Wim Van den Wyngaert]

And the block is 512 bytes.

What can you do with sh mem/cac/fu ?

[Ian Miller.]

"What does "Block IO" refer to in this context"

Consider this Example.

Transfer Size: Reads Read Hits Writes
1 Block IO: 1339139 1224267 624906
2 Block IO: 87599172 77137023 616565
3 Block IO: 6046985 5196849 181878

This saying there has been 1339139 read requests for reads of 1 512 byte block.
There has been 87599172 Reads for 2 blocks
There has been 6046985 reads for 3 blocks.

From this sort of data you can determine the most frequently requested size of read or write on your system. If you take this data and paste it into a spreadsheet you can plot histograms, calculate averages etc