VMS Backup takes forever to create the Save-Set

[Robert Atkinson]

We recently took delivery of some 160/320 SDLT tape drives.

As our backup system, TapeSys, writes each file to be backed up into a single save-set, I noticed that the backups were taking ages per file.

When I investigated further, I found that each save-set was taking around 30 seconds to create on the tape, even though the file was only 50 blocks.

When I check this against my TL891 (DLT8000), I still find that the save-set takes around 15 seconds to create.

What I would like to know is :-

a) Do you think these timings are normal
b) Is there any way I can speed up the creation of the save-set, as I cannot alter the files being backed up
c) Do anyone know the internals of how the tape drives actualy create the save-set

I have attached the log file for the SDLT test.

Any help would be appreciated.

Robert.

[Willem Grooters]

Robert,
I don't have experience with this type of tape drives, but I think these are typically designed for large-volume-backup in a data centre (or archiving). That is: High-density and high-speed - both could well be understatements.
High-speed also means it will take considerable time to slow down to halt, rewind to end-of-data, reposition and start to full speed before the next block can be written - all within the margins the tape can handle. My guess is that it will be considerable better if you backup large files (or groups) in stead of single small files.
Not that this repositioning for each file will count for the whole 15 seconds extra, but this adds up if done for each file. So if you have 100's of them....
I would consider backing up in larger chunks so you don't have to reposition on each file separately (by directory - as long as there is quite a lot of files held below)

Willem

[Ian Miller.]

Ensure you are using a large block size (65000) and enable compression. Also ensure the username used for BACKUP has big enough quotas (see VMS Sysman manual for recommendations - its important to get the relationship between the quotas right).

These these things ensure you can drive the tape drive in the way it was designed to go.

[Antoniov.]

Hi Robert,
I think Willen says right.
Backup one file per saveset is a wrong mode to do backup.
The saveset is a backup container of files; in saveset files are stored with full path, so you can restore it individually; this means there is not reason to backup separately.
Besides consider tape has block size very high (higher if tape device run quickly); so every file (saveset) on tape stay in a multiple of block (as on HD); using large block size (i.e. 65000) means every file (also 50 block little) write 65000 block on tape.
I read your log and I updating batch to build a backup command instead backup single files.
If will you agree I can post an example.
Bye
Antoniov

[Robert Atkinson]

Thanks for your responses.

Unfortunately, you cannot use comma-seperated file lists under TapeSys. If I want to backup file-a, file-b and file-c (as opposed to a whole disk or directory), each file must be specfied seperately, so they each go into a single save-set :-

$ TLFILES_1 :== SY0:[LIVE.DAT]MULIMP.MAS
$ TLFILES_2 :== SY0:[LIVE.DAT]MULPUB.MAS
$ TLFILES_3 :== SY1:[LIVE.DAT]*.INT;*
$ TLFILES_4 :== SY1:[LIVE.DAT]*.SOR;*
$ TLFILES_5 :== SY1:[LIVE.DAT]*.NUL;*
$ TLFILES_6 :== SY1:[LIVE.DAT]WBSHDET.MAS
$ TLFILES_7 :== SY1:[LIVE.DAT]WBSHINV.MAS

I end up with over 600 savesets on a tape, which equates to 1 hour of tape movement, excluding any actual writing!

I am aware of how to make a backup efficient, high block sizes, no CRC checking, account quotas, etc. What I can't do is make the tape write the save-set header any quicker.

Having said that, I'm going to test reducing the block size to 2048, and see if the save-set is written any quicker. I'm not sure if it will help in the long run, but at least I'll have a better idea what the drive is up to.

Robert.

[Antoniov.]

Hi Robert,
You can also use /CACHE=WRITE to run quicly.
See HELP MOUNT
Bye
Antoniov

[Martin P.J. Zinser · Accepted solution]

Hello Robert,

doing the 600 savesets on the tape will not only be detrimental to the time you need to perform the backup, but also will wear down both the tape media and the drive faster than normal. Have you considered to put the single files first into a container on disk (either a on-disk backup saveset or e.g. a Zip-file) and then to backup this container file? Or since Tapesys does support full directories for backup, copy them in a backup directory on disk and then do the backup of this whole directory.

Also I guess you will not be able to put really 160 GB of data on the tape in the mode you currently use...

Greetings, Martin

[Willem Grooters]

Robert,

In addition to Martin's reply - I also considered that but since that requires an extra disk and extra time, I suppressed mentioning it. Now that he did, I will: Backup the files onto a (huge, cheap) disk (HP has 146Gb (ATAPI) disks) and backup that whole disk to tape. That's the way HPs' 'near-line' storage works, I think. There could well be a way to access (and retrieve) each file individually, so that might be a solution.

[Burkart Beat]

Hi Robert

Please! Give me one good reason for having every file in a single backup-saveset!

I hope you just don't know how to extract one single file out from an OpenVMS Backup Saveset. I cannot see any other reason for your approach...

I personally do every backup with /IMAGE, compared to /SELECT=(...) for a subset of all files, it is up to 10-times faster.

/IMAGE allows you as well to restore a single file from a saveset

Hope this helps
Beat

[Martin Johnson]

Your problem is TapeSys and it's limitations. There is no reason to backup one or a couple of files to a a saveset. There is a lot of overhead associated with small savesets. First, the streaming tape drives can't stream, which means that they must stop and back up. This alone can triple your backup times. Second, the overhead of creating all those extra saveset container files. That can almost double your backup times.

Question: Why are you backing up only certain files? If the files not backed up are not needed, why are they on your system? If they are needed, why aren't they backed up? Maybe they don't change, but the way you are doing things, it would be quicker to back them up. It would also be a LOT quicker to recover your system from backup if ever the need arises. If all the files are backed up all the time, all you need is one saveset (the latest) to restore your system.

The easiest way to back up your system is one disk to one saveset. That way if you lose a disk, all the data is contained in one saveset. By doing an /IMAGE backup, the volume data is saved also.

I recommend changing TapeSys to backup each disk to a saveset, not selected files.

HTH
Marty