ARCserve r11 hardware compression 1

[koltes]

Hello,

I'm using ARCserve r11 with a HP SureStore DAT40 tape drive. When I want to attach a session to a tape already containing data that is compressed using software compression, ARCserve doesn't let me turn off hardware compression and turn on software compression for the additional session because the tape isn't empty. Hardware compression isn't an option because data encryption is used.

Does anyone know how to disable hardware compression in this case?

Regards,
Andreas Koltes

 

[davidmichel]

It is not possible to have a tape mixed with and without compression. Your only choice is to use a different tape.

 

[koltes]

But that's the case at the moment. The first session is compressed using software compression with hardware compression turned off. When I added the second session, ARCserve Manager automatically turned off software compression with a warning message because hardware compression was enabled.

 

[Cyklops]

You can only set hardware compression in the device manager on 'blank media' (ie new or erased tapes). Once you put another tape in the tape drive ARCserve automatically wil turn back to hardware compression (which is always enabled on the tape drive). I have never understood the functionality of this setting in the Device manager and never use it.

regards

 

[koltes]

I did exactly this to disable hardware compression for the first session but when I inserted the tape the second time, it was enabled.

Perhaps hardware compression wasn't successfully disabled for the first session but the manager said it was disabled and I'm sure that it used software compression for the first session. Perhaps both hardware and software compression were used for the first session but the manager didn't report that.

Another idea: Is there a way to force software compression even if hardware compression is enabled?

 

[davidmichel]

If hardware compression is enabled software compression will be automatically disabled.

 

[Cyklops]

You can force it by disabling the compression on the hardware side, mostly by adjusting jumper settings (check the manuals or ask your hardware vendor for this..
If there are issues with compression on encrypted data I think this will count for both hardware and software compression as they both use algorithms to compress data.

regards

 

[koltes]

I did some tests and think that I have a problem with the tape drive. When I disable hardware compression in the manager and format the tape the manager says that hardware compression is disabled but in reality hardware compression is still turned on. I ejected the tape and reinserted it and hardware compression was enabled.

Software compression is applied before data encryption, so it will work together with it. Hardware compression will never work with software encryption because encrypted data has nearly zero redundancy (except for the metadata that is written unencrypted to the tape).

However, thank you for your comments

 

[koltes]

I found a solution for the problem. It was indeed an error in the tape drive. I updated the firmware from the old four years old version to the current version and everything is fine now.

Disabled hardware compression now stays disabled.