No hardware compression, only with NetBackup

[letournp]

I already posted in an other thread, but I don't find it anymore, so here is my problem once again!

Problem :
When I use NetBackup to make a backup, there is no hardware compression (close to none: I managed to put upto 106Go on a tape)

But when I use BackupExec with the same file selection, I manage to put upto 166Go on the tape.

How are the Software used to backup and the hardware compression related ?



Setup :
Hardware
DELL PowerEdge 2850, 2.8Ghz
Adaptec 2100S SCSI adapter
Twisted cables with terminators
1 X IBM HH LTO ULTRIUM-1 100/200G Lates firmware "N2CG"
Latest drivers "HP Ultrium ..." 1.0.2.0 (2003-01-08)
Software
Veritas BackupExec 8.60 Rev. 3878
Type of compression : Hardware (if available, else software)
Veritas NetBackup 5.1 MP1
I tried with/without the compression (wich is software)
Note: both software installed on the same machine

 

[Flave]

Hi

The compression is always made by the drive, never through the
application. If you see the possibility for compression somewhere on the master server setting, this means to compress the data on the client side before sending it to the network. But its only use is on poor network performance (2GB link or so) and it needs a lot CPU performance on the client side.
Check the veritas web page to get the right settings for your tape drive(s) (there are some device description files you probably need to put under /usr/openv/volmgr/database/ or ?:\progra~1\veritas\volmgr\database).

Furtheron you need to know how NetBackup writes data to the tapes (concerning retention times, etc.).

Cheers
Flave

 

[letournp]

Hi Flave,

I know that the compression check box in NetBackup is ofr software compression on the client side. Slowing the backup, taking more CPU, but reducing the total bandwith used.

The problem is with hardware compression.

Using both products, on the same machine, I get 166Go with BackupExec and 106Go with NetBackup (then ask goes for a second tape)

BUT, I'm completely puzzled this morning, a test from yesterday took the whole 127Go I gave to NetBackup
And last night backup took the whole 135Go

What append during that time ?

 

[Flave]

Hi letournp

Need to take of now - will get back to ya tomorrow.
But what you mean by 166/106/127 and 135 Go ? Is it GB ?

As i already said, NetBackup doesn't do anything actually, it just writes a tar file to tape.
....but will get backup 2 u 2morrow with detailed info's.

Cheers
Flave

 

[lenski]

There are some issues which can effect the amount of data on the tape. To maintain speed of data transfer some software will write blanks to the tape so that the tape is kept moving even if the cach is empty. This drematicly improves the speed of write to the tape as in most systems the tape is the fastest element. Backups can be very slow if you can not feed enough data to the tape as it then has to stop and restarts. That is why it's done, but of course by writing blanks there is less room for data.

 

[letournp]

Hi to both of you,

Flave : 166Go, (it's french, sorry for the mistake) should have read 166GB

Lenski : Ho ! that would explain why I managed to put 127GB the other day (Since the test was data coming directly from the server and was probably faster)

I lied a bit in the description, telling I had a DELL 2850. I have the server, but I did not made the switch yet, since I'm waiting for the external rackmount kit for the tape drive. Maybe the actual server (100M/b) isn't fast enough for the tape. ...

K then, I'll use the old tape drive enclosure (which is not RM) we have in stock to make the machine switch asap and will tell you if it worked.

Pascal,

 

[lenski]

There is a switche which can be used to control this practice. But I can remember where it is.

 

[letournp]

Hi everyone,

My server hardware migration is completed.

A test for a full backup just completed and there is 135 Gb of data on the tape.

I can't explain the exact reason why it is now working, but, ... whatever, it is !