I think most of the confusion with hardware compression is caused by the ads
and spec. sheets. They should put in a few extra words about the 2 to 1
compression of DLT hardware compression as being a statistical average based
on common backup scenarios. Hardware compression is a compression algorithm
similar to compress, gzip, etc. that is programmed into the tape drive
function. If you are backing up mostly binary files you probably won't get
much compression at all (maybe none). If you are backing mostly ascii files
you will probably see greater than 2 to 1. Backing up lots of sparse files
you could see huge compression ratios. If you use or have access to gzip,
read it's man page for some good high level information on compression.
-----Original Message-----
From: David A. Chapa [mailto:david AT datastaff DOT com]
Sent: Monday, February 19, 2001 5:16 AM
To: Dustin Scharf
Cc: Stephen Dvorak; 'David A. Chapa'; clifford thurber;
veritas-bu AT mailman.eng.auburn DOT edu; nbu-lserv AT datastaff DOT com
Subject: Re: [Veritas-bu] RE: [NBUADV-L]: compression and DLT 7000
Clifford:
After talking with my client over the weekend and
finding out what they were backing up, I found that
they were some db files. These files had a lot
of 'white space' or otherwise called sparse files that
when backed up will compress much more than the
advertised drive spec.
David
Quoting Dustin Scharf <dusty AT veritas DOT com>:
> Absolutely. For example, at a previous job we
rutinely (sp?) got 15:1
> compression from a an application using a cobol
database... tons of white
> (blank) space in the files. we would get well over
300GB of data on a
> single DLT tape. Conversely, try backing up a bunch
of zip files or
> already
> compressed files... you won't get near the 70GB.
>
> Dustin
>
> Dustin Scharf
> Veritas Education Services
> dusty AT veritas DOT com
>
>
> -----Original Message-----
> From: Stephen Dvorak [mailto:sdvorak AT veritas DOT com]
> Sent: Friday, February 16, 2001 3:40 PM
> To: 'David A. Chapa'; clifford thurber;
> veritas-bu AT mailman.eng.auburn DOT edu
> Cc: nbu-lserv AT datastaff DOT com
> Subject: RE: [NBUADV-L]: compression and DLT 7000
>
>
> The 70GB limit on DLT 7000 drives is assuming 2:1
compression. The drive
> is
> capable of producing greater compression rates than
this. Thus, if the
> data
> is highly compressable, the drive should be able to
get better than 2:1.
> Steve
>
> -----Original Message-----
> From: David A. Chapa [mailto:david AT datastaff DOT com]
> Sent: Friday, February 16, 2001 2:33 PM
> To: clifford thurber; veritas-
bu AT mailman.eng.auburn DOT edu
> Cc: nbu-lserv AT datastaff DOT com
> Subject: RE: [NBUADV-L]: compression and DLT 7000
>
>
> I've seen the same thing at another customer's
site...the Veritas SE that
> was onsite before me said that it may be due to some
HIGHLY compressable
> data...I'm not sure I know what that means since I
haven't had an
> opportunity to research it further.
>
> David
>
> <><><><><><><><><><><><><><><><><><><><>
> David A. Chapa
> Consulting Manager
> DataStaff, Inc.
> 847 413 1144
> http://www.consulting.datastaff.com
> ---------------------------------------
> NBU-LSERV AT datastaff DOT com - Adv. Scripting
>
> -----Original Message-----
> From: owner-nbu-lserv AT datastaff DOT com
> [mailto:owner-nbu-lserv AT datastaff DOT com]On Behalf Of
clifford thurber
> Sent: Friday, February 16, 2001 2:05 PM
> To: veritas-bu AT mailman.eng.auburn DOT edu
> Cc: nbu-lserv AT datastaff DOT com
> Subject: [NBUADV-L]: 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
>
> ------------------------------------------------------
-
> NBU-LSERV AT datastaff DOT com - Advanced NetBackup Scripting
> http://www.consulting.datastaff.com/adv_script_site
>
>
> ------------------------------------------------------
-
> NBU-LSERV AT datastaff DOT com - Advanced NetBackup Scripting
> http://www.consulting.datastaff.com/adv_script_site
> ------------------------------------------------------
-
> NBU-LSERV AT datastaff DOT com - Advanced NetBackup Scripting
> http://www.consulting.datastaff.com/adv_script_site
> _______________________________________________
> Veritas-bu maillist - Veritas-
bu AT mailman.eng.auburn DOT edu
>
http://mailman.eng.auburn.edu/mailman/listinfo/veritas-
bu
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
David A. Chapa
Consulting Manager
DataStaff, Inc.
847 413 1144
-------------------------------------------------------
NBU-LSERV AT datastaff DOT com - Advanced NetBackup Scripting
http://www.consulting.datastaff.com/adv_script_site
|
