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тАО08-04-2009 07:53 AM
тАО08-04-2009 07:53 AM
Tape AT&T and Berkeley-style
-----------------------------------------------------------------------------------------
c0t0d0BESTnb, tape0_BESTnb - Best density, no autorewind, Berkeley style
c0t0d0BESTb, tape0_BESTb - Best density, autorewind, Berkeley style
c0t0d0BESTn , tape0_BESTn - Best density, no autorewind, AT&T style
c0t0d0BEST, tape0_BEST - Best density, autorewind, AT&T style
According to man mt(7):
" When a file open for reading (only) is closed and the no-rewind bit is
not set, the tape is rewound. If the no-rewind bit is set, the
behaviour depends on the style mode. For AT&T-style devices, the tape
is positioned after the EOF following the data just read (unless
already at BOT or Filemark). For Berkeley-style devices, the tape is
not repositioned in any way.
"
My question is about BEST(for example c0t0d0BEST, tape0_BEST)- Best density, autorewind, AT&T style(positioned after the EOF). I don't get it... the tape is positioned after the EOF and then it is rewound?! The first movement is redundant,isn't it?
When we have autorewind, what is the difference between BEST and BESTb?
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тАО08-04-2009 08:48 AM
тАО08-04-2009 08:48 AM
Re: Tape AT&T and Berkeley-style
The word "BEST" indicates that with this device file, the highest possible capacity format will be used. This will also include data compression if it is supported by the device.This will also include data compression if it is supported by the device.
The "b" character shows that the tape drive will follow the Berkley style instead of AT&T.
The character "n" shows that the tape will not be rewound at the end of the operation.
Hope the query is answered.
Regards,
Sooraj
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тАО08-04-2009 09:11 AM
тАО08-04-2009 09:11 AM
Re: Tape AT&T and Berkeley-style
It appears you're right. From mt(7), I don't see any difference. Unless there are other operations besides the documented close(2) that are affected.
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тАО08-04-2009 09:13 AM
тАО08-04-2009 09:13 AM
Re: Tape AT&T and Berkeley-style
Pete
Pete
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тАО08-04-2009 10:06 AM
тАО08-04-2009 10:06 AM
Re: Tape AT&T and Berkeley-style
@Dennis - 10x Dennis
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тАО08-04-2009 10:15 AM
тАО08-04-2009 10:15 AM
Re: Tape AT&T and Berkeley-style
:) .. As Pete told I missed the important part in the q itself, However
Dennis, Here you can see
Berkeley and AT&T functional modes differ in ├в read only├в close functionality. IfBerkeley identifies a ├в read only├в close on a device file minor number, the tapemedia position will remain unchanged by the device close operation. If AT&Tidentifies a ├в read only├в close on a device file minor number, the tape media will berepositioned just after the next tape filemark (the start of the next file). Normally,Berkeley mode should be used.
The last sentence is meant for only "no rewind". ?
Regards,
Sooraj
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тАО08-04-2009 02:00 PM
тАО08-04-2009 02:00 PM
Re: Tape AT&T and Berkeley-style
That's how I read mt(7). But it applies for the whole paragraph.
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тАО08-04-2009 05:48 PM
тАО08-04-2009 05:48 PM
Re: Tape AT&T and Berkeley-style
"Only raw, no-rewind Berkeley-type devices should be specified. This type of device will not reposition the tape upon close."
For the mt command, AT&T device files can really mess up tape positioning.
Now all the above only applies to tape positioning commands. Backup programs like fbackup bypass all automatic tape driver features and manage the tape position with driver calls.
Bill Hassell, sysadmin