insufficent Data on DLT IV Tapes

[tschons]

Hello

We are using ArcServe2000 SP3 on a Windows2000SP3 Server. We have an Quantum DLT4000 and are using DLT IV Data Cartridge 40/80GB. I enabled hardwarecompression on the Quantum.
Now my problem: ArcServe used 6 Tapes to backup 140GB. When I looked on tapes they have between 18-33GB.
exactly: 1. 18GB,2. 22GB,3. 33GB,4. 27GB,5. 32GB, 6.rest.
Any ideas why some tapes have just about 20GB?

Thanks a lot for any help or ideas!

cu tschons

 

[ReddLefty]

Hardware compression can only compress to a certain point. If you backup up compressed data of any kind (ZIP, RARs, MP3...), this will greatly affect the amount of data that can be stored in your tape.

When they say 40/80, they mean (from the data's point of view): 40 Gigs of COMPRESSED DATA or 80 Gigs of UNCOMPRESSED DATA can be stored on the tape.

Another way of looking at it: Your tape is formated at 40Gigs and the hardware compression tries to stuff as much as it can while compressing it onto the tape.



"In space, nobody can hear you click..."

 

[davidmichel]

The DLT IV tape is a 40/80gb tape.
The DLT 4000 tape drive is a 20/40gb drive.
This means even though the tape can hold 40gb of non-compressed data the drive can only write 20gb of non-compressed data to that 40gb tape.
DLT 7000 is 35/70gb
DLT 8000 is 40/80gb
So you can use DLT III tapes and get the same capacity per tape.

Regardless you should at least be getting 20gb on tape. Is tape 1 18gb of data backed up or written to tape? The difference is that for each file there is overhead, which I can not imagine taking up 2gb on tape but it is still a factor. So for example if it was 18gb of 25k files it would be a lot of over head if it was 18 1gb files it would be very little. Another possibility is soft write errors. This happens when a write fails the tape is automaticly moved to the next block and retried. If the write is completed then it is a soft error and will not stop the job but will take up space on tape. Soft & hard errors should be reported in the Database. Another possibility is streaming. When the data flow coming in to the tape buffer does not match what is going out to the drive, the drive has to either stop start or stream. The stop start is tough on drives and the streaming results in blank space on tape.

 

[xenotec]

DLT technology works on Blocks.. If the DLT is set to 32 or 64 kb and most of the files on the server are WORD documents that equal roughtly 1 KB, you are going to get let information committed to tape.

While the below is for older version of ARCserve it can still apply

http://support.cai.com/techbases/asnt/NASNT412.html

NOTE: if you change the block size you will be unable to restore from older backup tapes unless you change the block size back to the original setting

 

[tschons]

Thanks a lot for all your help!!! now many things are more clear for me!