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surestore dlt vs80-compression question

Frequent Advisor

surestore dlt vs80-compression question

I've got a surestore dlt vs80, thats supposed to get 40GB native and 80 compressed. I'm uing arcserve for the back program. When I check the arcserve backup log, it says that "software compression is disabled to hardware compression" Ok, I understand that hardware will override. But how can I tall how much compressin i'm getting? Arcerver won't be able to tell what teh tape drie is doing, I don't think. and the drive itself doesn't seem to do any of the logging. currently we're backing up just over 50GB and its prompting for a second tape, which it didn't used to do. How can I tell ho wmuch compression i'm getting so that I know if I need to start goin to a 2 disk scheme.

thanks all!

Trusted Contributor

Re: surestore dlt vs80-compression question

Hello Justin,

I am not sure about arcserv, but hope the information given below help you in some way. But more of it is related to fbackup (hpux commands).

How Hardware Compression works

The amount of data that can fit on a tape depends on the type of data being backed up and the utility doing the backup. Ascii files compress well, binaries compress some, compressed files will actually expand when compressed again

"compressed files will actually expand when compressed again". The HPUX command compress(1) uses a similar algorithm to
that used by the data compression hardware in the drive.

So while taking the backup of compressed file use non-compressed device file.

While taking the backup of non-compressed files use compressed device file.

Incase if you want to know how much /arhives filesystem will expand while doing the hardware compression, type the following commands.

# find /archives/* | xargs cat | wc -c ==> Will give the present size of the files

# find /archives/* | xargs cat | compress | wc -c ==> will give the expand size when if use compression for already compressed files(please note here size will increase than the original size)

I tested in my machine, please find the difference

# find ssh.gz |xargs cat | wc -c ==> original file (9.2MB)
# find ssh.gz | xargs cat | compress | wc -c ==> When i want to use with compress it expanded to 12.4MB
(Here i am able to see the difference of 3.2mb for a single file)

As i have said, it is related to fbackup and hpux drives only. you can always cross check.

Frequent Advisor

Re: surestore dlt vs80-compression question

Thanks for the info albert!
Olafur Orn Olafsson
Occasional Advisor

Re: surestore dlt vs80-compression question

Hi Justin

I found this on the HP web somewhere:

An example of some typical data compression ratios that could be expected when using different forms of data on an HP tape drive are given below (although, of course, these are only a guide as the ratio will be unique for each data compressed):

Compressed man pages .9 to 1
Gallery drawings 1.3 to 1
DOS binaries 1.5 to 1
C object code 1.6 to 1
S700 HPUX binaries 1.7 to 1
General PC apps 2.0 to 1
Lotus spreadsheets 2.1 to 1
Microsoft(R) Word documents 2.2 to 1
mail 2.3 to 1
ME3- drawings 2.4 to 1
C source code 2.4 to 1
HPUX man pages 2.4 to 1
Empress database 2.5 to 1
Oracle Database 4.0 to 1
Uncomp .tiff images 4.2 to 1
Island DTP documents 6.0 to 1
MPE Turbo image 6.8 to 1

Frequent Advisor

Re: surestore dlt vs80-compression question

thank you for the ratio comparisons.