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Compression on T9940A FC tape drives

Mike Lewis_1
Occasional Visitor

Compression on T9940A FC tape drives

I am getting no compression when writing to T9940A FC drives from HP Superdomes, whether using 0mnb or 0nb devices. I have already trawled through the forums and knowledge bases, also I've spoken to HP themselves. The only comment I've seen was in a reply to a forum message that implied that not all capabilities of the T9940A drives were supported by HP yet. However I can't find the same message again.

Even a definite response such as "You cannot get compression on these drives from HP servers" would give me "closure" on this problem.

The backup software is Veritas NetBackup DataCenter 3.4 with a Sun master server and a mix of HP and Sun Media Managers. The Sun Media Managers DO get compression. I am convinced it is a driver issue rather than a NetBackup configuration problem.


Nick Clifton
If it's not broke ... doesn't mean it can't be improved!
harry d brown jr
Honored Contributor

Re: Compression on T9940A FC tape drives

What are you using to determine wether you are getting compression or not?

live free or die
Live Free or Die

Re: Compression on T9940A FC tape drives

The T9940A drive is not officially supported with the stape driver. Can you configure the drive to work in 9840 emulation mode? The driver actually tries to identify the device's identifiaction to decide what operation is most appropriate. Also, in the mean time you can try creating this device file with the following mksf command:

mksf -d stape -I -u -n -b D9840C

This will create a device file asking the driver to set the drive to the 9840 density with compression on.

To verify this setting, run the following command:

mt -f status

You should see whether compression is set there.
Mike Lewis_1
Occasional Visitor

Re: Compression on T9940A FC tape drives


Sorry for the delay, the God of Documentation is looming over me!
Using the NetBackup script I have checked the sizes of the FULL tapes. Also my colleague, who is a whizz at interpreting the NetBackup logs, was the person that highlighted this problem.

HP tapes vary from 56.39Gb to 56.66Gb
Sun tapes vary from 85.11Gb to 131.42Gb

Hope this is of some help.


Thanks for the suggestion, as luck would have it there is a StorageTek engineer on site at present, he is checking the drive settings. It may take some time to test this as I need to get any changes authorised by many people.

Can I just check your suggestion about the mksf, do you mean this may work even if the drive is NOT set to emulate 9840?

Thanks for the help so far.
If it's not broke ... doesn't mean it can't be improved!