[NBUADV-L]: RE: [Veritas-bu] compression and DLT 7000

We recently saw this very clearly with some AIT-2 vs DLT evaulation that
we did.

We found that the AIT-2 gave rock solid compression consistently
(100-120Gb on 50gb tape).
However DLT compression the same data set was very random (35-118 on 35
gb tape).
I think this may have to do with throughput issues to the DLT.
I believe the AIT-2 technology is a lot less sensitive to those issues.
Of course that is only a guess as our data was less than conclusive
regarding the root cause.

Dennis


> "Weaver, Paul" wrote:
> 
> Clifford,
>         I have seen this, especially when backing up Oracle
> databases.  It really depends on the type of data that is being backed
> up as to how much compress the drives actually can do; the 70GB is
> assuming 2:1 compression.  Not being an oracle dba, it looks like
> Oracle has a lot of "empty" space in it's tables, depending on how it
> is configured I guess, so this space which still gets counted as KB is
> easily compressed into almost nothing.  This is my opinion, though.
> 
>         We have had no issues with restores from these backups/tapes.
> 
> Paul Weaver
> 
> -----Original Message-----
> From: clifford thurber [mailto:cthurber AT concretemedia DOT com]
> Sent: Friday, February 16, 2001 3:05 PM
> To: veritas-bu AT mailman.eng.auburn DOT edu
> Cc: nbu-lserv AT datastaff DOT com
> Subject: [Veritas-bu] compression and DLT 7000
> 
> Hello,
> We are using Netbackup 3.2 on Solaris 7 with Quantam DLT 7000 Drives.
> We
> have the following line in our st.conf file
> DLT7k-data =    1,0x36,0,0x9639,4,0x84,0x83,0x0,0x85,3;
> Which I believe denotes that we have 70GB of storage in  compressed
> mode. I
> also believe that this is the theoretical limiton DLT 7000's using
> compression. The confusing part is that when I run the media list
> report I
> see tapes that are 87GB, 129GB and 111GB. Can someone tell me how this
> is
> even possible? Veritas was not able to give me an answer to this?
> Thanks in
> advance I will summarize.
> Clifford
> 
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