Problem with Saveset manager and Backup/data=compress

[Laurence Gillett]

I have been using saveset manager with no problems for the past year or so, to copy savesets on disk to an SDLT320.

However I recently started using using BACKUP/data=compress to create the disk savesets (weekly) for some of the larger disks
but saveset manager does not recognise the compressed savesets as valid savesets.

An extract from the log of the backup and the log of saveset manager is below:

BACKUP LOG:
$ show time
20-JUL-2007 19:22:23
$ backup/record/data=compress data_disk:[000000...] -
BACK_DISK:[FULL]full_data_disk.bck/SAV/ignore=(interlock)/exclude=(*.lan)
%BACKUP-I-COMPRESS, data compressed by 56%
%BACKUP-I-STARTRECORD, starting backup date recording pass at 21-JUL-2007 08:36:42.47
$!
$ show time
21-JUL-2007 08:44:23


SSMGR LOG:
$ saveset copy/lo/all BACK_DISK:[FULL]*.bck sdlt1:*.*/block_size=65024
ERRORS terminal option enabled
EVENTS terminal option enabled

...

%SAVESET-I-INVSAVESET, BACK_DISK:[FULL]FULL_DATA_DISK.BCK;1 is not a valid save set

The savesets which were not compressed copy OK onto the tape.

I only started using data=compress on the backup after reading about it on this forum.
I know it's not a 'supported' or documented feature but it does the job I want!

Does anyone have any experience of this problem (lack of campatibility between BACKUP and saveset manager)

I am running on Alpha OpenVMS V8.3
Backup V1.8
Save Set Manager V1.8

Laurence.

[Volker Halle]

Laurence,

BACKUP explicitly does not support writing compressed savesets to tape. Compressed savesets have variable length records instead of fix-length records.

This would most likely be the main reason for saveset manager having problems with compressed savesets.

Volker.

[Hoff]

Out of curiousity, does the BACKUP data compression (which is still undocumented?) get you better data compression than the native SDLT compression?

I'd be mildly surprised if the SDLT drive managed to get anywhere compressing the compressed data, and you might want to poll the drive -- somebody posted a tape capacity probe tool here within the last week or so -- to see if you're actually using less or more tape; if you're benefiting from host compression.

By what I mean here, you may only receive the 160 GB native capacity out of the SDLT 320 drive, if you're tossing already-compressed data at the drive. (The drive should be smart enough to shut off compression should the results of drive-level compression increase the quantity of data written to the tape medium.)

[Jon Pinkley]

Hoff>>>"somebody posted a tape capacity probe tool here within the last week or so -- to see if you're actually using less or more tape; if you're benefiting from host compression."

That was in http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=1143795

See the note dated Jul 18, 2007 01:03:41 GMT for a zipped version, or Jul 21, 2007 05:26:07 GMT for one that is just saved as text, and that entry also has some examples of usage (but the display is being affected by the forum's blank space compression).

NOTE WELL: As written, the command procedure will not work for SDLT320, because it explicitly checks for the device types, and works only for the types of drives I have. I would guess that it would work for DLT320, but I don't have one, and we have moved to LTO-3. You have the "source" in DCL, and you can take the check for type of tape drive out to see if it works.

P.S. Does anyone know where I can find the documentation for HP LTO drive SCSI commands? I would like to write something that can do something similar with LTO-3 drives, but I have been unsuccessful in finding a document with HP's Ultrium 3 (960) command set.

[Hoff]

What current SCSI command(s) are you using?
I've spent a long time deep in the T10 SCSI materials and lobbing SCSI commands at devices, and there exists the standard command set and the vendor-specific command set. You're usually fairly safe in the standard commands (though details and implementations can vary wildly), but the vendor-specific stuff can vary far more wildly, in terms of its availability, stability, documentation, and even vendor-level compatibility.

[Jon Pinkley]

Hoff>>>"What current SCSI command(s) are you using?"

http://www.citi.umich.edu/lab/admin-notes/dlt4000productmanual.pdf

Page 5-135

If the tape drive receives an unsolicited REQUEST SENSE, it returns sense data with the appropriate values in the End of Media (EOM), Sense Key, Additional Sense Code, and Additional Sense Code Qualifier. The positional information provided reflects the logical position of the tape drive. The tape drive returns information based on the non-diagnostic data in its buffer as well as the data on tape medium. Additionally, bytes 25 through 28 contain the amount of tape to be written in 4 KB blocks.

Page 5-136 has Figure 5-70 REQUEST SENSE - Data Format, where bytes 25-28 are referred to as "tape remaining".

At the bottom of pate 5-138, the description is "Tape Remaining This field reports the amount of tape remaining in 4KB (4096 bytes) blocks."

I just let SYS$ETC:SCSI_INFO do the work, and search the output for "sense bytes" and convert it from 4K blocks to MB.

The LOG SENSE READ/WRITE COMPRESSION RATIO page (see page 5-52) allows you to see how much data has been transferred between the host and drive, and how much was transferred to tape. That would be useful information if you wanted to know how much the data in a specific saveset was compressed, but it isn't in general very useful to determine the amount of remaining capacity on the tape.

15 or 20 years ago we bought a TTi packaged Exabyte drive that displayed remaining tape on a 4 digit 7 segment LED display, and I really missed having that information when we started using DLT drives. Once I found the SCSI manual, I started to write a program to do the dirty work, but while playing with SCSI_INFO, I saw that the needed data was available, and just did the quick & dirty as a temporary workaround. Like most quick & dirty things, it was never replaced, because it worked well enough, and there were always other things to do.

What I am looking for is a manual for the HP Ultrium 960 that is similar to the DLT4000 manual. I can't find one.

I am hoping there is a way to determine the remaining capacity on the LTO-3 tapes.

[Hoff]

I don't see a manual for this model, though here's a detailed manual for another Ultrium drive that has details on command packets and layout...
http://www.tandbergdata.com/artikeldatenbank_v1.1/download/doc/SCSI_Reference_with_LTO_Gen_3.pdf
It'd be worth comparing what you get back with this Ultrium drive, after lobbing a few commands at it.