Don't forget almost all tape writing software is writing some kind of
files to the tape. Between each file there are gaps, markers etc. So
there is always a % overhead. If you write ANSI tapes 80-block tapes
(i.e. 1 file on disk = 1 file on tape) like with a 'copy' command the
overhead is very large, especially if the files are small. You get a gap
between blocks, and another between files.
Most backup software writes some kind of 'save-set' which is a wrapper for
the actual files. I think for NetBackup the storage unit maximum fragment
size is the number to watch that sets the size of the files it writes.
This is typically set to 2GB (2000MB in the GUI), as many o/s cannot
handle disk files bigger than this, and if you wish to use backup-to-disk
that is a limit. There is also the tape buffer size (SIZE_DATA_BUFFERS),
which determines the block size written to tape. For DLT that is often
64K, for LTO often 256K.
You can see that for a 100G tape (ignoring compression by the tape
hardware) you get 50 files @2GB, and 1.6M blocks @64k. So there can be an
overhead, 10-15% may not be bad. I don't know how big the gaps are. The
tape capacity will be calculated as if there was one continuous bit stream
on the tape.
So - use 2000MB fragments in the storage unit, and as big a
SIZE_DATA_BUFFERS as your hardware will support - but be careful with the
latter as it affects memory usage, and you are most likely to tune that
for performance, not tape capacity.
William D L Brown
veritas-bu-admin AT mailman.eng.auburn DOT edu wrote on 07/06/2004 17:22:26:
> You got 98G on a DLT tape. That sounds very full to me. They're
> only 40G Native. That's better than 2:1. What makes you think it's
> not "fully utilized"?
>
>
> -M
> -----Original Message-----
> From: Hubler, Daniel [mailto:daniel.hubler AT cobalt-corp DOT com]
> Sent: Monday, June 07, 2004 10:17 AM
> To: Donaldson, Mark - Broomfield, CO; veritas-bu AT mailman.eng.auburn DOT edu
> Subject: RE: [Veritas-bu] Not fully utilizing tapes
> Here is some output from available_media (I deleted some stuff).
> The tapes in question are: BWU010 & BWU011 (about half-way down the
list):
>
> ====================================
> /home/xxxxxx$ available_media
> media media robot robot robot side/ ret size status
> ID type type # slot face level KBytes
>
----------------------------------------------------------------------------
> test-STARS-backup-1 pool
>
> BWU004 DLT NONE - - - 1 15461204
ACTIVE/MPX
> BWU047 DLT NONE - - - 1 60600121
ACTIVE/MPX
> BWU048 DLT NONE - - - 1 42365962
ACTIVE/MPX
> BWU051 DLT NONE - - - 1 409520 ACTIVE/MPX
> BWU036 DLT NONE - - - - - AVAILABLE
> BWU037 DLT NONE - - - - - AVAILABLE
> BWU038 DLT NONE - - - - - AVAILABLE
> BWU039 DLT NONE - - - - - AVAILABLE
> BWU040 DLT NONE - - - - - AVAILABLE
> BWU052 DLT TLD 0 15 - - - AVAILABLE
> BWU002 DLT NONE - - - 1 102795955
FULL/MPX
> BWU003 DLT NONE - - - 1 102507391
FULL/MPX
> BWU008 DLT NONE - - - 1 100847104
FULL/MPX
> BWU009 DLT NONE - - - 1 113999174
FULL/MPX
> BWU010 DLT NONE - - - 1 98881611 FULL/MPX
> BWU011 DLT NONE - - - 1 94186203 FULL/MPX
> BWU012 DLT NONE - - - 1 125489547
FULL/MPX
> BWU013 DLT NONE - - - 1 128797560
FULL/MPX
> BWU021 DLT NONE - - - 1 126117420
FULL/MPX
> BWU022 DLT NONE - - - 1 123570554
FULL/MPX
> BWU033 DLT NONE - - - 1 121749425
FULL/MPX
> BWU041 DLT NONE - - - 1 125116945
FULL/MPX
> BWU042 DLT NONE - - - 1 121046181
FULL/MPX
> BWU043 DLT NONE - - - 1 110269596
FULL/MPX
> BWU044 DLT NONE - - - 1 96771748 FULL/MPX
> BWU045 DLT NONE - - - 1 115321358
FULL/MPX
> BWU046 DLT NONE - - - 1 105210453
FULL/MPX
> BWU053 DLT NONE - - - 1 126886727
FULL/MPX
> BWU054 DLT NONE - - - 1 122242787
FULL/MPX
> BWU055 DLT NONE - - - 1 116116379
FULL/MPX
> BWU056 DLT NONE - - - 1 107045233
FULL/MPX
>
> =================================================================
> =================================================================
> -----Original Message-----
> From: Mark.Donaldson AT cexp DOT com [mailto:Mark.Donaldson AT cexp DOT com]
> Sent: Monday, June 07, 2004 10:57 AM
> To: daniel.hubler AT cobalt-corp DOT com; veritas-bu AT mailman.eng.auburn
> DOT edu
> Subject: RE: [Veritas-bu] Not fully utilizing tapes
> How are you determining this? Can you snip some output here?
> -M
> -----Original Message-----
> From: veritas-bu-admin AT mailman.eng.auburn DOT edu [mailto:veritas-bu-
> admin AT mailman.eng.auburn DOT edu]On Behalf Of Hubler, Daniel
> Sent: Monday, June 07, 2004 9:50 AM
> To: veritas-bu AT mailman.eng.auburn DOT edu
> Subject: [Veritas-bu] Not fully utilizing tapes
> NBU v4.5 on Solaris 8.
> What would cause NBU to stop writing to a tape before the tape is full?
> One of our large backup jobs consumes about 12 tapes.
> 2 that participated in the middle of the job flow were left 10-25%
empty.
>
> Daniel Hubler
> Database Administrator
> TrustSolutions, LLC
> Milwaukee, WI
> daniel.hubler AT cobalt-corp DOT com
> phone: 414-226-5391
> pager: 877-580-0731
> pager email: 8775800731 AT my2way DOT com
> page via internet: www.my2way.com
>
> The information contained in this electronic message may be
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