> -----Original Message-----
> From: Joshua Baker-LePain [mailto:jlb17 AT duke DOT edu]
> Sent: Wednesday, August 02, 2006 5:04 AM
> To: McGraw, Robert P.
> Cc: amanda-users AT amanda DOT org
> Subject: Re: tapetype question
> 
> 
> On Tue, 1 Aug 2006 at 1:53pm, McGraw, Robert P. wrote
> 
> > How is length calculated? I would think that the length should be closer
> to
> > 400G if hardware compression is on.
> 
> Ah, the hardware manufacturers have brainwashed you well!  ;)  They'll be
> so pleased.
[McGraw, Robert P.] 

Not brainwashed but not knowing what amtapetype was trying to do. Maybe we
should talk about physical and logical tape. The physical tape can only hold
~200GB, the logical tape can hold X depending on the data and the
compression scheam. Kind of like Nup printing, 1 physical page can hold X
logical pages. 

I see now that amtapetype is trying to find out how much a physical tape can
hold, where I am interested in what a logical tape can hold based on my
data. I know this is relative to my site and data.

This was a good read for me, http://en.wikipedia.org/wiki/Linear_Tape-Open
"Technical Features" and the link IBM's LTO RedBook - EVERYTHING you wanted
to know...

Thanks very much for your help. 

> 
> In addition to the other comments posted, keep in mind that LTO is a
> different animal when it comes to hardware compression than most other
> hard drives.  The hardware compressor is "smart", meaning that it won't
> try to compress incompressible data.  Most tape drives running in hardware
> compression mode dumbly throw everything through the compressor.  If the
> data is already gzipped, e.g., or is otherwise incompressible (like
> amtapetype's random data) this actually *expands* the data and you
> end up with less data on tape than the native capacity.  LTO doesn't do
> that.  That's why, despite amtapetype's warning that you were using
> hardware compression, the tape size still came out right (200GB).
> 
> With my LTO3 drives, I leave them in hardware compressed mode, but still
> use software compression on some DLEs.  My users are pretty good (not very
> good, mind you) at compressing their data on disk to save space, so the
> tapelength I give amanda is only slightly bigger than the 400GB native.
> Some nights I'll get 110% tape usage, though.
> 
> --
> Joshua Baker-LePain
> Department of Biomedical Engineering
> Duke University
[McGraw, Robert P.] 

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

And here is my results from 

./sbin/amtapetype -o -t LTO2HWC -e 200g -f /dev/rmt/1n

Writing 2048 Mbyte   compresseable data:  38 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
wrote 6422528 32Kb blocks in 98 files in 7358 seconds (short write)
wrote 6455296 32Kb blocks in 197 files in 7737 seconds (short write)
define tapetype LTO2HWC {
    comment "just produced by tapetype prog (hardware compression on)"
    length 201216 mbytes
    filemark 0 kbytes
    speed 27315 kps
}

I am in the process of trying to find out how to turn off hardware
compressing for the Solaris 10 OS.

Thanks

Robert

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