On Tue, Nov 25, 2003 at 10:46:10AM +0100, Martin Oehler wrote:
> Hi!
>
> Am Mo, 2003-11-24 um 13.54 schrieb Gene Heskett:
> > On Monday 24 November 2003 03:46, Martin Oehler wrote:
>
> [...]
> > Doing this to a tape also should tell you whether or not the drives
> > internal compression is in use, which for amanda, should be turned
> > off as that hides the true size of the tape from amanda.
>
> I need to work with hardware compression because I have 6 hours
> at night to execute my backup before people are starting to change
> files. With software compression, backup doesn't finish in time
> because the compression itself takes to long (I think an amanda
> mode that first moves the data completely to the backup server
> and then starting to compress, freeing the backed up boxes, would be a
> good solution. The "online compresssion" eats a lot of time).
>
> > Amanda
> > counts bytes sent to the drive after any gzip is applied, and if the
> > drives compressor is on, the data normally will grow slightly and
> > amanda may hit EOT thinking it still has 10-15% of the tape left.
>
> The Quantum drive hardware compression is completely manageable
> via the mt command. I'm now turning the compression off before starting
> the tape test and turn it back on for backup. When I'm finished
> with tuning the amtapetype test
I make this comment based on your using hardware compression for
your amdumps/amflushes. If you are using amtapetype for its
original purpose, determining the capacity of the tape, the
effort of running amtapetype is not really needed. The vendor
can give you the "native capacity" of the drive/format and
amtaptype generally comes within a few percent of this. The
vendor will also give a capacity with compression, typically
2X to 2.6X the native capacity. The actual compression you
realize during tape writes depends on the nature of your data.
So the actual capacity, for your data, is an unknown and has
to be guessed when creating a tapetype definition in amanda.conf.
You do know the upper and lower bounds however, native capacity
and advertised capacity with compression. Neither of these
values needs amtapetype to determine. So an amtapetype run
is unneeded to create your tapetype definition.
> I want to use this inside my backup
> script, so each tape is tested before amflush starts (I'm using amanda
> with holding disks).
What does that mean? That you run amdump with no tape in the
drive, forcing the entire dump to the holding disk? Then at
some later time you do an amflush? I ask as I too am using a
holding disk (big enough for about 2 wks of dumps) but I seldom
run amflush.
--
Jon H. LaBadie jon AT jgcomp DOT com
JG Computing
4455 Province Line Road (609) 252-0159
Princeton, NJ 08540-4322 (609) 683-7220 (fax)
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