How to enable the HP DAT72 Tape Drive's hardware compress function?
[238 byte] By [DavisTai] at [2007-11-26 11:03:45] 
I did a backup test, found the HP DAT72 Tape Drive just can backup 36GB data. The transfer rate about 3MB/s, so it looks like no harware compressd, but I don't know how to enable it, could anyone please tell me? Thanks in advance.
# 1
Its usually controlled by the device name you use to access the tape.
If you look in /dev/rmt, you'll see all the tape devices.
The ones with c in their name are the compressed devices.
So if you save to /dev/rmt/0 your writing to the uncompressed device.
If you save to /dev/rmt/0c you get compression.
robertcohen at 2007-7-7 3:17:40 >
# 2
Thanks. I just done another test before I read your reply. I have another HP DAT72 tape drive attached to the other Sun server(Netra240, same the 1st server), and I executed the command 'tar cvf /dev/rmt/2n /data', however, the /data is about 49 GB, and the backup speed is about 4.23 MB/s...
Since there's 'media write error' in the 1st Netra240 server, and the tape drive [Clean] LED is lighted, so I put the clean tape before I did backup. And I found this situation, it can't do hardware compress!!
And may I ask if using '/dev/rmt/0c', does it mean software compress or hardware compress?
TKS!!
DavisTai at 2007-7-7 3:17:40 >
# 3
The "c" device is to enable hardware compression.The "n" means not automatically rewind the tape.robertcohen at 2007-7-7 3:17:40 >
# 4
So, it' really strange, the same OS version, the same tape drive model, the same command, however, different result...DavisTai at 2007-7-7 3:17:40 >
# 5
You could check for customisations in /kernel/drv/st.confIf thats not it, I can't think of what else it could be.robertcohen at 2007-7-7 3:17:40 >
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