On Tue, Aug 01, 2006 at 01:53:45PM -0400, McGraw, Robert P. wrote:
> Presently I am using an SDLT220 tape drive with hardward compression turn
> on. I have a new LTO2 tape drive and I really do not want to run the
> amtapetype program if someone else has already done this. 
> 
> Here is my LTO2 drive:
> 
>       Product Type: Tape Drive
>       Vendor ID: 'HP      '
>       Product ID: 'Ultrium 2-SCSI  '
>       Revision: 'F63Z'
>       Attached Changer: No
>       SerialNumber: 'HUL5M02595'
>       MinBlock:1
>       MaxBlock:16777215
>       Ready: yes
> 
> I am trying to decide if I want to compress with software or hardware with
> the new drive. I see the advantages and disadvantages of each. 
> 
> 
> Here is an lto2 tapetype that matches my unit.
> 
> -bash-3.00$ /usr/sbin/amtapetype -e 200g -f /dev/nst0 -t Ultrium2
> Writing 4096 Mbyte compresseable data: 40 sec
> Writing 4096 Mbyte uncompresseable data: 350 sec
> WARNING: Tape drive has hardware compression enabled
> Estimated time to write 2 * 204800 Mbyte: 35000 sec = 9 h 43 min
> wrote 6422528 32Kb blocks in 98 files in 6420 seconds (short write)
> wrote 6422528 32Kb blocks in 196 files in 6719 seconds (short write)
> define tapetype Ultrium2 {
> comment "just produced by tapetype prog (hardware compression on)"
> length 200704 mbytes
> filemark 0 kbytes
> speed 31300 kps
> }
> 
> 
> In the above case hardware compression was turned on. 
> 
> How is length calculated? I would think that the length should be closer to
> 400G if hardware compression is on.

I would think it would be closer to 900G if you feed it nothing but
ascii text files.

I would think it would be closer to 250G if you feed it nothing but
jpeg picture files.

But we "know" if you feed it uncompressible data it is 200.704G.

amtapetype uses "random" data which is essentially uncompressible.
It determines how much data your tape can hold.  How well you can
squeeze your data with gzip, or your tapedrive can squeeze it,
amanda can't know ahead of time.

I have to run now, if no one else writes about solaris tape devices
I will tonight.

> 
> I am running Solaris 10 on the amanda server. I ran the first part of
> tapetype with /dev/rmt/1n(c) where "n" is no rewind and "c" is compression.
> I did not specify the "c" or "u" for compression, yet I got "WARNING: Tape
> drive has hardware compression enabled".
> 
> zorn->[46] > ./amtapetype -o -c -e 200g -f /dev/rmt/1n -t Ultrium2
> 
> Writing 2048 Mbyte   compresseable data:  37 sec
> Writing 2048 Mbyte uncompresseable data:  76 sec
> WARNING: Tape drive has hardware compression enabled
> Estimated time to write 2 * 204800 Mbyte: 15200 sec = 4 h 13 min
> 
> zorn->[51] > ./amtapetype -o -c -e 200g -f /dev/rmt/1cn -t Ultrium2
> 
> Writing 2048 Mbyte   compresseable data:  37 sec
> Writing 2048 Mbyte uncompresseable data:  76 sec
> WARNING: Tape drive has hardware compression enabled
> Estimated time to write 2 * 204800 Mbyte: 15200 sec = 4 h 13 min
> 
> 
> Any ideas on how to turn off compression?     
> 
> Thanks
> 
> Robert
> 
> _____________________________________________________________________
> Robert P. McGraw, Jr.
> Manager, Computer System                 EMAIL: rmcgraw AT purdue DOT edu
> Purdue University                         ROOM: MATH-807
> Department of Mathematics                PHONE: (765) 494-6055
> 150 N. University Street                   FAX: (419) 821-0540
> West Lafayette, IN 47907-2067            
> 


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