Save set file size

[Lionel Liu]

Hello there,

I use the following command to create a save set file

$ BACKUP/IGNORE=(INTERLOCK)/LABEL=(RSBKUP) DKC0:[000000...]*.*;* MKE500:RS_DAT.SAV/SAVE_SET/NOREWIND/log/block=65024

Then I use the following command to check the save set file size

$mount/ov=id mke500:
$dir mke500:[000000...]*.*/size

it display the RS_DAT.SAV save set file size is 16547 blocks

So the save set file size would be

16547/(2*1024)= 8.07 M

Is that right? For save set file, are they use the same way to calculate the size as the disk file?

thanks

Lionel

[Ian Miller.]

each of the 16547 blocks will be 65024 bytes big (compared with the disk block size of 512).

(16547*65024)/(1024*1024*1024) = 1Gb

[Travis Craig]

Lionel,

You should expect your save set to be quite a bit larger than the total size of the files you saved into it, because BACKUP adds error detection and correction codes. 10%-20% larger is probably reasonable.

--Travis Craig

[Lionel Liu]

Thanks very much for your reply

If I am using the following command without /block=65024

$ BACKUP/IGNORE=(INTERLOCK)/LABEL=(RSBKUP) DKC0:[000000...]*.*;* MKE500:RS_DAT.SAV/SAVE_SET/NOREWIND/log

So the system will use 32256 as default block size

the save set file size would be

16547*32256/(1024*1024)= 509 M

Is that right? 32256 is the system default block size for save set file,correct?

Thanks again

Lionel

[Bojan Nemec]

Lionel,

For tape the default block size is 8192 bytes. 32256 is the default block size (record size) for disks. See HELP BACKUP /BLOCK_SIZE.

Bojan

[Lionel Liu]

Sorry I get a little bit more confused

Can somebody give me a example how to calculate the disk and save set file size
?

what is the system default block size for disk file and what is the system default block size for save set?

Thanks again

Lionel

[Joseph Huber_1 · Accepted solution]

Disk-block-size is -in VMS- 512 bytes, so if You have the number of blocks (with directory/size), the file size is nblocks*512 bytes.

For tape files it is in principle the same, just the block-size does vary: file size is nblocks*blocksize bytes.

The block-size of tape files (like savesets), if not known, You can get using DIRECTORY/FULL:
$ mount tape: !NOT mount/foreign
$ directory/full tape:
You get the file-size in blocks , and the record length = blocksize for fixed length records (backup savesets are fixed length records).

[Robert Atkinson]

If you're trying to work out how much you can get onto the tape, remember to take into account compaction.

Most drives support compression up to 80%, so if the tape was initialised with /MEDIA=COMPACT, this will have a big effect.

Robert.

[Joseph Huber_1]

For the sake of completeness, why is a directory/full necessary for a save-set on tape, isn't a directory/size enough ?

Directory/size gives the size as number of blocks, but the blocksize is not known.
One can write many savesets to tape, each with different blocksize. So one needs the 'record size' from directory/full to calculate the save-set-size.

[Daniel Fernandez Illan]

Lionel
You can obtain blocksize using:
Backup/list MKE500:RS_DAT.SAV/SAVE
and see this information on head information of save set file.
Saludos.
Daniel