Hardware Compression does not appear to be working

[RobVar]

I have an ageing Dell Poweredge Server which, until recently, had a DDS-3 tape backup drive. I had been able to squeeze upto 18Gb on a 12/24 tape using BackupExec v7.0.
After the drive failed it was replaced with a DDS-4 unit. It is reported as Archive Python 06240-XXX (f/w 8110) though I believe it is an IBM badged drive (not 100% sure).

Despite trying alternative driver (stdat4.sys) supplied and the 4mmdat.sys obtained from bntidrv.exe, and making sure use hardware compression if checked in the drive properties in BE device manager, I only appear tobe able to store about 20Gb on the DDS-4 tapes. This seems to suggest that hardware compression is now not working. This seems to be borne out by a tape diagnostice TapeRx which, when the "Enable Compression" command is actiones, reports that it cannot do so.

Has anyone had similar experiences?

The server is running NT4.Sp6a and BE v7.0 Rev662 Single Server Edition.

Many Thanks

Robert Varley

 

[DTracy]

We have an HP DDS4 tape unit that I had the same questions about. I used the tape diagnostic utilites to test and found it had the capibilities of 2 or 3:1 compression but when I saved data it did not compress unless the data exceeded the compression levels. In other words, unless I had more than 20 GB of data it would not use 2:1 and until I exceeded 40 GB it did not use 3:1, I don't know why. You might try backing up more than 20 GB and see what happens.




Best Regards,
David Tracy

 

[RobVar]

David

Thanks for replying.

I guess I should have said that the reason I knew compression wasn't working was because BackupExec was asking for a second tape to be inserted when the amount backed up reached 20Gb. So yes I have already tried more than 20 Gb of data.

Interestingly, I tried s/ware compression last night and got all my data on the one tape with a reported ratio varying between 1.3:1 and 6.4:1. I worked out the average as about 1.62:1 which is quite respectable.

Interesting too is the total bytes verified as compared to the total backed up. That more or less matches the average compression ratio achieved.

Still would like to try hardware though if it is possible.

Regards
Robert Varley

 

[MattOP]

Hey Robert Varley,

Did you find a fix for the 2 tape problem? I've got the same on an IBM x225 server with Seagate DDS4 drive

 

[RobVar]

Hi MattOP

No I have not yet got to the root of the problem. I have been able to get round it though, as I mentioned above, by using software compression. I does seem to be able to achieve a respectable average compression of about 1.7:1.

It looks like I've got the "experts" stumped, or it is such a simple answer that no-one can bear to embarrass me by stating the obvious.

 

[MattOP]

Robert,

mines slightly diff problem to yours, mine says
Compression Configurable
Setting Compression to On

but then still only backs up 22gb to a 20/40 DD4 tape drive.

 

[justin2000]

mattop - you are getting compression, it goes to 22gb - so it is working

what are you backing up? if the files are already compressed then they won't compress any more - may even be bigger on the tape.

 

[MattOP]

Thanks Justin,

Well I just ran another backup with Software Only for compression and it finished successfully without asking for 2nd tape.

I wonder if the default block size settings for compression are wrong for this drive.

When running job with hardware compression it makes no mention of what compression was achieved but with Software it does.