On Sat, May 24, 2003 at 12:17:30AM -0400, Gene Heskett wrote:
> On Friday 23 May 2003 23:47, Mathias K�rber wrote:
> >Paul Bijnens <paul.bijnens@x...> wrote:
> >> IMPORTANT!
> >> You also have to know that, no matter what you had executed as
> >> setting for the compression of your drive, if you READ a tape,
> >> the drive will set itself to what the mode of the tape was. If
> >> you insert a tape written with hardware compression, disable the
> >> drive hw compr by "mt compression off" (verify with "mt
> >> status"), then read the tape, it's back in hardware compression!
> >> (verify again with "mt status"). This implies that if you want
> >> to overwrite a tape with the other mode, you may NOT read
> >> anything on the tape after setting the mode.
> >
> >This is the part that worries me. Amanda does perform a tape-read
> >at the beginning of amdump etc.
> >While that usually is no problem with amdump (as only labeled
> > tapes should be used anyway and hopefully they are of the correct
> > type assuming that tapes have been labeled withthe correct
> > compression setup), amlabel itself also performs a read and may
> > switch back to uncompressed if one tries re-labeling a previously
> > uncompressed tape to compressed or vice-versa.
>
> Thats exactly what will happen in almost all instances from my
> experience.
>
> >I would think a -c option to amlabel which makes it set the
> > compression just before writing the label would be useful. If
> > could name a program (shell script) which does the actual setting
> > (such as mt or stinit). Other tools in the amanda suits might
> > benefit from this too.
>
> Change that to a -c true/false, and it would be a winner. The
> problem with that is that the various drives take various commands
> to effect that, so it might be required to have a preset file,
> built by the user, that contains the required command syntax to do
> that to *his* drive. It would also require a bit of must read
> documentation, and with some users, thats always going to be a
> problem due to a general lack of RTFM. In particular the noobie is
> going to be asking a lot of why can't amlabel just work, when in
> fact it cannot find the syntax file the user hasn't generated.
Kinda tough to do on a system such as mine which doesn't have
commands or calls to change compression settings. It is done
on the "open" call to the tape drive (and driver) by selecting
a device name. Like you call nst0 or st0 to select no/rewind.
How do you change that behavior after opening the drive?
Of course that is also the reason I don't suffer from the change
upon read problem you have.
> >> amtapetype from 2.4.4 does a write without a read (and will
> >> detect hw compression if still on :-) ).
>
> What does this portion of its report look like?
An error message and exit. No report.
--
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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