Question for SLS saveset

[Davor_7]

Hi expert,

i'm new VMS guy, and i found a strange thing.
our system run the SLS2.9G for backup
we use DLT IV 40/80 tape and the data will be backed up in a saveset during the job.
when the data is beyond 100G,it still can be backed up into the tape...
does that mean the saveset has a compression function when doing the backup?
so 100G data will be compressed into 70G(example) before written into the tape?

[Wim Van den Wyngaert]

Compression depends on how well your data can be compressed. All modern drives compress by default and indicate this with a LED.

Wim

[Jan van den Ende]

Davor,

second possibility: _IF_ the data your are BACKUPing includes PAGEFILE.SYS, SWAPFILE.SYS and/or SYSDUMP.DMP, those files are normally "Marked NOBACKUP". (you can see it with DIR/FULL).
In that case only the Headers go to tape, just a few blocks. For the difference, look at the sizes of those files.

Just for completeness, it _IS_ possible to mark other files as well, although it is not often done.

fwiw

Proost.

Have one on me.

jpe

[Ian Miller.]

Is the SLS backup job doing a backup of everything from the disk or just the files that are changed. Best idea would be to list the contents of the tape and see what is there.
You can also look at the backup qualifiers specified in the SLS *_SBK.COM file.

[Davor_7]

Miller, to answer your question.
it's full backup, instead of incremental.
all the device/files are in the backup list....

[Steven Schweda]

Saying "full backup" is not as good as
showing the actual BACKUP command, but unless
you specify "/IGNORE = NOBACKUP" (which would
be unusual), the data in those page, swap,
and dump files will not really be saved, and
that can be a big tape saver.

[Thomas Ritter]

This is an extract of an SLS generated backup command.


$ -
BACK/STOR=V2SLS/RELEASE_TAPE/LIST=_MBA3989:/FULL -
DSA2:/IMAGE/NOALIAS/IGNORE=(LABE,INTERLOCK)/MEDIA_FORMAT=COMPACT/RECORD/RELEASE_TAPE/BLOCK=65534 -
_$1$MKD400:DSA2.BAK/PROT=(S:RW,O:RW,G:R,W:R)/NOASSI

Running version

%SLS-I-VERSION, Storage Library System for OpenVMS, version V2.9H

Extract the backup command from your log file and post.

[Wim Van den Wyngaert]

All documents mention reduction to 50% of the original size. I read that as up to 50%.
But if your data files hold lots of spaces or binary zeroes (as in initialized db files that have lots of space unused) I guess compression result could be better than 50%.

How did you check the size ? dir/siz=used I hope.

Try mounting the tape and do a dir/siz of the saveset. Then we'll have the size of the save set.

Wim

[Robert_Boyd]

I would think that if you're backing up the entire collection of disks, that you will have multiple savesets on the tape.

The easiest way to find out is to do these commands:
if you're logged in as SYSTEM, change your default directory to a non-search list value to avoid having DIRECTORY scan the tape twice.

$ SET DEFAULT SYS$SPECIFIC:[SYSMGR]
$ MOUNT/OVER=ID :
$ DIRECTORY/SIZE=ALL :*.*;*/OUTPUT=SAVESET_INFO.LIS

Robert

[Davor_7]

Wim,
our SLS job will create LIS file to show how many files are backed up.
and i can get the total block for those file :)

[Davor_7]

robert,

you mean this way could be used to track how many real size the tape hold the data?

[Ian Miller.]

yes, there is a summary line at the end of the listing file
Total of X files, Y blocks

[Robert_Boyd]

Davor,

Yes -- the method I suggested will display the actual size of the savesets in tape blocks. Be careful to distinguish this from disk blocks. The tape blocks will be whatever size used by BACKUP to write to the tape. The easiest way to verify that is to look at the LIS file or to use BACKUP to list one of the savesets to see what value it used for /BLOCK. It may or may not be the same as was specified on the command line because BACKUP adjusts the value to the closest "correct" size, and the maximum it will write to tape I believe is 65024.

The listing files you have are only partially useful because they list the sizes of the input files being backed up. If you look for pagefile and swapfile entries it will still list the total size of the file. In my experience the only way to know for sure how big a saveset is requires looking at the tape with DIRECTORY to see.

Years ago I did some experimenting to see how closely the listing files tracked the size of savesets on tape. Generally speaking they are accurate when discounting the files marked NOBACKUP. The challenge is to discount for these files -- some systems have many more of them than the basic set on the system disk.

Robert