25 Gigs won't fit on 40 Gig tape

[flo2980]

Last week our backup started to fail because it was asking for another tape. The drive is an HP Surestore with 40 Gig DAT tapes. The OS is Windows 2000 Server. Everything has been fine for a few months. I checked the compression is set in the job descriptions and on the drive itself. I tried a full erase and got the same result. The job gets to about 18 Gigs and spits out the tape. Any suggestions?

Thanks for all the advice in the past!

 

[SQLBill]

Are you appending to the tape or are you always overwriting?

If you are appending, the tape will fill up and need a new one.

40 GB brand new tape.
Save 15 GB to the tape, 25 GB free space left
Save 15 GB more, 10 GB left
Save 15 GB more, ooppss, not enough room, 10 GB gets saved and you need a new tape for the last 5 GB.

If ANY part of a backup is on the tape and there isn't enough tape left, the backup job CANNOT overwrite just the beginning of the tape. Overwrite means erase the whole tape. It can't do that if part of the backup job is on that tape, so it needs a second tape to finish.

-SQLBill

 

[flo2980]

The tapes are set to overwrite. Would another consideration be not to use the media catalog?

 

[SQLBill]

Just to make sure I understand you...the tapes are set to always overwrite and you don't allow append?

-SQLBill

 

[Prydonian]

Is the 40Gb figure the native storage or the compressed? If the tape is labelled as 20Gb/40Gb then it is only going to hold 20Gb w/o compression. AND in my experience, you will NEVER see that 40Gb storage amount in this universe. Regardless of what type of compression you're running.

Mike

 

[flo2980]

Everything seems to be going OK now and has for the last few days. Same data, same tapes. Go figure....

Thanks for the advice!

 

[mattjurado]

As Prydonian says, sometimes compression works okay, and if you have a 40gb compressed limitation, you might get 30-35 gb on that tape. Then again, you might near or reach 20gb, and have it spit the tape out at you. If you have more problems, try a brand new tape for a week. If it works okay, replace the tapes. They have a finite life expectancy, and I have seen their usability deteriorate over time.

Matt J.

Please always take the time to backup any and all data before performing any actions suggested for ANY problem, regardless of how minor a change it might seem. Also test the backup to make sure it is intact.

 

[figmatalan]

Well, some data compresses well. On the Legato server I look after, some of the LTO-1 tapes (100Gb Native, 200Gb compressed assuming the 2:1 that everyone quotes) have nearly 800Gb of data on.

I can only imagine that these are not db files or things like that but have a lot of plain text in them which does compress very well. 4:1 compression is not something you see often on large systems, your more likely to get something like 1.25:1.

 

[dkediger]

Things like AutoCad files will compress very well, as they are essentially text files.

Word/Excel stuff compress to a moderate to high level.

Graphics and zip/other compressed archives tend to actually increase in size slightly if they are run through a second compression routine.