How can I check the capacity of my tape and/or drive?

[mtmazzitello]

I am using Backup Exec 9.1 on a Windows 2003 Server.

My tape drive is a Quantum DLT-4000 and my tape media is Sony "DLTtapeIV" which claims to have a capacity of "20/40 GB on DLT4000" (20G uncompressed, 40G compressed). It says 1828 feet also.

The problem I am having is that even though I specify "overwrite media" and to use hardware compression and software compression if hardware is not available, when the backup job gets to a byte count of about 23G or so it prompts for a new tape.

With the above described drive and media should I not be able to get close to 40G of data on a single tape?

In Backup Exec the "properties" of the tape media says it has a capacity of 19.1G with a 2.00:1 compression ratio - does this mean the tape can actually only hold 19G of data? Does this mean the software is seeing it as a 19.1G tape even though it is supposed to be a 20/40G capacity? I don't know where to find any capacity information for the drive, all the Backup Exec properties shows is that it is indeed a Quantum DLT 4000 device.

How can I determine if it is the tape or the drive or the software that is limiting me to 23G per tape?

Thanks,

Mark

[Ken_Putnam]

2:1 compression is a marketing thing, not an engineering thing. see http://seer.support.veritas.com/docs/199542.htm

I generally use about 1.3:1 as a rule of thumb. 23 GB on a 20GB tape is about 1.15, so that IS on the low side

You can try a run with Software Compression only selected. The ratio won't be exactly what HW would be, but it will be close.

As far as the Veritas Display of Tape capacity, until the tape volume has been written to until the End-of-Tape marker, BackupExec really doesn't know what the capacity is.

[mtmazzitello]

Thanks for the info, I didn't realize that 40G actually means "UP TO" 40G capacity. The tapes are brand new so worn media shouldn't be an issue. I'll try out some different compression options and see what I get.

Still it would be nice if there was a way to check the actual capacity prior to running a 4 hour backup job so I would know if it's going to require a tape change in the middle of it.

[Deepali_Badave]

Hello,

Thank you for the update.

The Backup Exec does not give the estimation of the data can be written on
a media. Usually, we consider it equal to the native capacity of the media.
However, you can write more data on the media than its native capacity, if
compression is used. This is due to the varied types of data that are found
in most environments, each data type has it's own compression ratio and
therefore no standard is achieved for the compression ratios that result.
For example; database data generally compresses the least, and regular text
files can compress the most.



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deepali

[Sheetal_Risbood]

As per our previous reply, marking the case as assumed answered and moving it to answered questions pool.