Storage Capacity & Compression

WH

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Jan 13, 2004, 1:57:24 PM1/13/04

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Hope this question doesn't seem to trivial but....

Am using an Adic FastStor DLT 7000. Using Sony DLT IV tapes. Using Veritas
BackServ for Netware ver 8.5.
Reading a few websites shows that these tapes hold 35G uncompressed and 70
compressed.
All my backup jobs on this server are marked to use hardware compression and
I find that when a job reaches around 35G that it rolls over to the next
tape. We do all of our calculations to determine tape usage based on this
35G per tape.

If I were to enable Software compression (in Veritas BackServ) would I then
be able to fit 70G per tape.

Sorry if this is a dumb question :-p. Still new to me.

Thanks,

Dave Lunn

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Jan 13, 2004, 5:49:13 PM1/13/04

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> If I were to enable Software compression (in Veritas BackServ) would I
then
> be able to fit 70G per tape.

No.

You will wind up with something less under ideal circumstances, and maybe
<35 gig if the data is already compressed on the server. Under ideal
circumstances you'll see about a 2:1 ratio. Normal useage is IMO always
less except when compressing uncompressed Db files.
--
Dave Lunn
NSC SysOp
http://support-forums.novell.com

WH

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Jan 14, 2004, 9:38:23 AM1/14/04

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Dave,

Thanks for the reply

So can I take from that answer that my actual tape is always going to hold
about 35G worth of data ?
ie
If I have a 70G file and I back it up to tape it will take 2 x 35G tapes,
with NO compression.
If I choose compression it will basically (in absolute ideal conditions)
compress the 70G file into a 35G file and store that on 1 x 35G tape.

In both situations the tape i really only holding 35G of data, the
difference i in what you do with the data before it is written.

Thanks again for the response. If I can finally understand this I be very
grateful.

Thanks,

Wayne Hansen

"Dave Lunn" <dlu...@SPAMmyrealbox.com> wrote in message
news:JB_Mb.90$zt3...@prv-forum2.provo.novell.com...

Mike

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Jan 14, 2004, 11:09:35 AM1/14/04

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WH wrote:

> Dave,
>
> Thanks for the reply
>
> So can I take from that answer that my actual tape is always going to hold
> about 35G worth of data ?
> ie
> If I have a 70G file and I back it up to tape it will take 2 x 35G tapes,
> with NO compression.
> If I choose compression it will basically (in absolute ideal conditions)
> compress the 70G file into a 35G file and store that on 1 x 35G tape.
>
> In both situations the tape i really only holding 35G of data, the
> difference i in what you do with the data before it is written.
>
> Thanks again for the response. If I can finally understand this I be very
> grateful.
>
>
> Thanks,
>
> Wayne Hansen

You also want to be aware that sometimes if you try and compress an
already compressed file (such as if compression is turned on for the
volume) that the result can be a larger file.

-Mike

Dave Lunn

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Jan 14, 2004, 10:31:55 PM1/14/04

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WH.

If you have a 70 gig file on the server and it is uncompressed on the server
then under ideal circumstances you will fit that into one tape.

If it is a 70 gig file and it *is* compressed on the server, it will
probably *not* fit on two tapes, and there will be a little bit spilling
over onto a third.