DAT40 don´t make compressing.

[David Paris AKA Mixmast]

Hello everyone,
i have several DAT40 with compressing enable, but the compressing don´t work.
I use NTBackup on Windows2003 and WinNt, the driver used for the DAT are native from the Windows.
Any one can help me with this problem.
I can send the LTT logs just send me the email.


Thanks.

[Patrick Wallek]

How do you know commpressing doesn't work?

How much data are you attempting to back up? What type of data is it? What tapes are you using?

[David Paris AKA Mixmast]

I´m gone try to obtain in more detailed the information that you ask me.
I´m just the hardware technician and i´m not the final user.

Thanks

[David Paris AKA Mixmast]

How much data are you attempting to back up?
38 GB
What type of data is it?
Data, Video and Data.
What tapes are you using?
The tapes are the 20GB from Imation and Sony.

Thanks for your help.

[rich pattison]

L&TT has a compression test - page 65 of the user manual shows how to use it:

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00713152/c00713152.pdf

If this runs OK - the drive is OK

Could be the data is already compressed (MPEG's/JPG's etc are a compressed format).
If your not sure - try "zipping" it up with something like 'Winzip' - this will show you what compression ratio is possible for your data.

[Anees Tajbhai]

Have a similar problem on a HP Storageworks DAT 40 USB external drive.

Also using windows backup. Backing up about 26GB of data (files, pictures, video) when it reaches about 20gb asks for a second tape. The data i am backing up is not compressed on the drive i select it from.

My question is why can i not go above 20gb regardless of data, even if it does not give me the exact 40gb compressed it should allow me more than 20gb

[rich pattison]

The native capacity of a DAT40 is 20GB, so it seems that for some reason the data is not being compressed. This can be for a couple of reasons - either the drive is not compressing, or the data cannot be compressed.

As I said earlier, L&TT will tell you if the drive compression algorithm is functioning. If you still aren't sure, L&TT will allow you to create data of a known compression ratio. You can then back this data up, and if it doesn't compress - you have a faulty drive !. Bad media/excessive re-writes of data can also reduce the total capacity of the media - again, L&TT will allow you to run a media validation check to see if there's a problem with your tapes.

If the data cannot be compressed, the drives internal compression cannot work!. A rough and ready check is to try another compression utility such as Winzip, to see if your data can be compressed, (but beware, hardware compression on the drive is not as efficient as software compression used by Winzip and other utilities).

Finally - are you sure Ntbackup is configured to compress? - from the GUI there is a box to tick, and command line there should be a \hc:on switch.

[David Paris AKA Mixmast]

I already make some tests with the L&TT and the result are that compressing is enable and the drive is OK.
I´m gone try to compress the data with software to see how much compressing is used.

Thanks to all.

[rich pattison]

Looks like there is an issue around NTBackup not handling DAT drive compression:-

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=42863&prodTypeId=12169&prodSeriesId=42863&objectID=c00059124

Maybe this could be the problem