Re: Virtual tape optimal image catalog entry size(s).

When dealing with tape images they can get larger up to the size specified when the image is created. They will NEVER get smaller on Disk. INZTAP and SAVXXX CLEAR(*ALL) both reduce the size of the data but the disk allocation does not go down. If you want the disk size to go down you must delete the image and build a new one.

Now you might say "This is terrible IBM, Why don't I get my space back when I initialize or clear the volume?" But if you understand this behavior you can use it to your advantage. If the space remains allocated then you know it's available when you re-use the volume for a subsequent backup. If it were cleared then the disk space could be used up and not available during backup. If you DO want to get the space back then simply DLTIMGCLGE and ADDIMGCLGE instead of INZTAP.

- Larry "DrFranken" Bolhuis

On 2/7/2012 2:51 PM, rob@xxxxxxxxx wrote:

I've got two stream file directories. One is 7.8GB and one is 13.5GB.
(subject to fluctuation). I want to same them to virtual tape and ftp
that data over to another system for processing. I will INZ the volumes
nightly prior to the backup. If I make too many image catalog entries, or
make them too big, then that just increases ftp time unnecessarily. If I
make them too small will it expand them? Today I did a ftp of two large
stream files
Name Size
VRT01 8,459,776K
VRT02 10,241,024K
1,583,382,689 bytes transferred in 174.085 seconds. Transfer rate 9095.459
KB/sec.
10,483,974,305 bytes transferred in 1179.655 seconds. Transfer rate
8887.320 KB/sec.
I did notice one thing, if I initialized them right prior to the ftp the
size changes:
Size of object data in bytes . . . . . : 12369
Allocated size of object . . . . . . . : 8662810624
Size of object data in bytes . . . . . : 12369
Allocated size of object . . . . . . . : 10486808576
and I resend these I get:
12369 bytes transferred in 0.000 seconds. Transfer rate 0.000 KB/sec.
12369 bytes transferred in 0.000 seconds. Transfer rate 0.000 KB/sec.
So, if I initialize them prior to backup, it will then only have that
nights size. Not sure about an unitialized overwrite.
On the receiving system
Size of object data in bytes . . . . . : 12369
Allocated size of object . . . . . . . : 32768
for both.


Rob Berendt