C1537 12/24 DDS3 - Win2k SBS - Compression (NOT!)

[Peter Moore_4]

Hi,

We have a C1537 with DipSwitch 1 - On and also DipSwitch 2 - on.

Dipswitch 3 - Off and then 4 - 8 are all on.

So.... Nothing new or troublesome there you may think, but....

We have updated the Firmware to L111 as suggested by LTT and the drive does backup data to tape. We also updated the Drivers to hpdat.sys also suggested by LTT.

However, the damned thing still refuses to compress data. The files are compressible using Winzip etc, but the drive WILL NOT store anymore than 2Gb on a 2/4 tape. (I know it is a 12/24 Drive, but ramping 2.5Gb of data to a test server is easier that sorting out 13Gb.

I am tearing my hair out.

Please, Please someone rescue me :)

Thanks...

Pete..

[Dave Dewar]

Hi Peter,

You switch settings are correct. If you use LTT to generate a support ticket you can examine this ticket and under the "drive configuration settings" bullet it will tell you if the drive thinks that compression is enabled. This will rule out any switch issue.

Next, you can use LTT to test data compression for you. If you go under the tests section there is a test called data compression that uses a known 2:1 compression data set to verify data compression is working properly.

If the two above things are correct, then it could be that you have disabled compression in you backup application, you don't mention what backup app you are using so I can't tell you how to check this.

Finally, 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. You currently have switch 1 and 2 set to on and so have 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.

Cheers,

Dave Dewar

[Peter Moore_4]

Hi Dave.

We are using the Standard Applet (NTBACKUP).

The LTT Test is compressing, so the drive is cool, also, it will compress on first use after boot up, but not after that.

The ticket says compression is on before the backup, but off following it.

I cannot believe that I have to reboot the server after each backup, that's just plain crazy.

Question - If I switch off Dipswitch 2, will the drive compress without letting the host know about it and if so, will the software be able to read the tape?

Thanks.

Pete..

[Dave Dewar]

Hi,

I don't believe NTbackup gives you an option to enable/disable compression, I have never found it anyway. It sounds like it is disabling compression before starting the backup, no idea why it would do this.

Hardware compression is ocurring within the drive and is effectively invisible to the host hence you will have no problems with NTbackup reading tapes by setting switch 2 to off, the data presented to the host whether hardware compression is on or off during a read is the same since the drive decompresses it as necessary. The switch will only prevent the host controlling whether it is on or off within the drive.

You might get an data expansion issue when trying to hardware compress already compressed data, but since NTbackup gives you no control over compression, then disabling host control is no great loss.

If you do upgrade to a more feature rich backup application later on, I would recommend reverting switch 2 back to on so that you can control hardware data compression via your software app, rather than having to change the switch setting each time.

Cheers

Dave Dewar

[Peter Moore_4]

Hi Dave.

I will try the Dipswitch Set to OFF and see what gives.

However, NTBACKUP from the commandline has a /hc:on-off setting, supposedly Hardware Compression.

We use this in our RSM.EXE scripts, but clearly it doesn' work.

I will let you know the outcome of the new test later today.

Thanks

Pete..

[Dave Dewar]

Hi Pete,

Well, I never knew that about the commandline option :) thanks.

Cheers,

Dave.

[Peter Moore_4]

I'm gutted.

The Dipswitch Set to OFF made no changes. The tape was spat out at 4Gb, so no compression.

This is driving me nuts.

Pete..

[Dave Dewar]

Hi,

When you say the tape was ejected after 4GB do you mean the same 2/4GB tape you were using to test this previously?

If so, then that means you have 2:1 compression occurring.

If you are using a 4/8GB tape and hence not getting any compression then there are a couple of things that might be going on.

1. The switch is not working, what does LTT say about compression status?
2. Your data is incompressible, already compressed such as jpegs or zip files and so further comrpession via hardware does not result in any reduction.
3. Your error rate performance is poor and hence your drive is wasting space doing rewrites.

You can check 2 but using the performance tools in LTT but measuring the actual compressionr atio of you target data.
You can check 3 by running write/read tests in LTT

Cheers,

Dave Dewar