DDS3 Not compressing using NTBACKUP on Win 2003 Server

[Karl Bjork]

DDS3 Not compressing using NTBACKUP on Win 2003 Server?

Already
1. Upgraded the drivers.
2. Upgraded the firmware.
3. Checked the compression ratio with HP Storageworks Library and Tools. 2.24:1. So it is okay.

Windows Server 2003 Ntbackup.exe will not compress. At 10GB it asks for another cartridge. Solution or suggestions would be welcomed.

Thank you.

[Karl Bjork]

Forgot to mention it is a HP C1537A 12/24GB internal DDS Drive.

[JohnWRuffo]

Have you tried issuing the jobs from the command line (script a batch job) using the /HC:on switch?

http://www.microsoft.com/resources/documentation/WindowsServ/2003/standard/proddocs/en-us/Default.asp?url=/resources/documentation/WindowsServ/2003/standard/proddocs/en-us/ntbackup_command.asp

[Karl Bjork]

Thanks. I have tried. It is also the default in the script created by ntbackup when running the wizard.

[JohnWRuffo]

Are you sure the data that you are backing up is "compressable"? Not big database files, PDF's and images...

[Karl Bjork]

I do not think so, it mainly data files. It is using the shadow copy function of server 2003. Although that makes me curious, what would happen if I disable it for one backup.

[Karl Bjork]

I tried without the shadow image. Same limitation. The drive is using hardware compression.

[Dave Dewar]

Hi,

Ok, first thing to bear in mind is that the maximum capacity of a DDS3 tape is 12GB. The 24GB figure comes from the assumption that you are using hardware comrpession and average a 2:1 compression ratio on the data you are backing up.

A couple of things could be going on here.

1. Your data is incompressible, say already compressed stuff such as jpegs and zips and your tape drive is operating with hardware compression enabled. Trying to compress already compressed data can lead to data expansion and hence you will get less that 12Gb since your compression ratio is will be a bit less than 1.

2. You do not have hardware compression enabled. Sometimes NTbackup does not enable hardware compression or even seems to disable it and maybe you are also losing capacity due to error rate issues with drive and hence achieving less than 12GB to tape.

Hardware compression should be on by default within the tape drive. There are some switches on the bottom of the drive, 2 of these control compression, switches 1 and 2. The standard shipment configuration is to have switches 1 and 2 set to on.

The link below describes the function of the switches on the bottom of the product.

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?locale=en_US&taskId=120&prodSeriesId=63916&prodTypeId=12169&objectID=lpg51068

Switches 1 and 2 control how data compression is enabled and controlled by host. Switch 1 and 2 set to on and mean data compression enabled and under host control so it could be that your host is disabling data compression for you. Setting switch 2 to off will enable data compression without host control, it will always be on.

Repeat your backup with different switch settings to force compression on and off and see if your backup size changes. This some provide some answers to 1 and 2 above.

To check the error rate performance of your drive run the write/read test in LTT.

I dont think NTbackup gives you an option to control hardware compression in drive. However, I have heard that you can send it a commandline option has /hc:on-off setting, supposedly to enable hardware compression.

For background reading, here are a link about compression in tape drives

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50244

Cheers,

Dave Dewar