DAT blocking factor & tapetool

DAT blocking factor & tapetool

Post by Pete Clin » Tue, 07 Dec 1993 21:15:50



Hi,
I've just got the Sun DAT 4mm tape drive, and having played with it
a while feel I've more or less got the hang of it.
The instructions say blocking factor of 96 is optimal, and putting
that with the b option in tar seems to work okay.  man tar, however
says 20 is the max value, and tapetool will not let me put in
anything bigger than 20.
Is there a way around this, or can I only use tapetool for DAT access
using inefficient blocking factors? (or have I, as has happened before,
missed something *completely* obvious...?)
In the meantime, back to tar and mt at the command line...

Pete.

--
Peter Clinch                            University of Dundee
voice 44 382 60111 x 2050               Department of Medical Physics
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1. Using dump: DAT drive density/blocking-factor

Can anyone tell me what blocking factor I should use for a DAT drive
(Sony SDT-S5000 - 16GB compressed/120m tape)?

The SunOS dump man page tells me what I should use for various old-style tapes,
and also for (what sounds like) a 2.3GB exabyte drive.  It also states that
126 is 'the maximum available with most drives'.  Is it a case of optimising
this for the type of file on the filesystem?

As for density, well I've done a rough calculation:-
16GB = 1.7e+10 bytes
over 120m (=12000cm) this equals 1431655.8 bytes/cm
*2.54*8 gives the bits-per-inch figure of: 29091246

Given that the figure given for the exabyte drive is 54000, this seems a
little excessive - is it right - or have I missed something vital?

Here are some timings for dumping the / filesystem (about 10MB)

b               d               time (min:secs)
---------       -----------     ---------------
126             29091246        08:20                   the correct default?
256             29091246        12:50                   a larger blocking-factor
126               100000        12:20                   back to 126, lower d
256               100000        12:40                   higher b, lower d
126            100000000         8:10                   d*3 (ish)

The tape-drive documentation claims a transfer rate of 366kB/s (uncompressed)
dunno whether the B means bits or bytes, but being pessimistic and assuming it
means bits, it should still save 10MB in just under 4 minutes...
Can anyone explain all this stuff so I'm not just trying random figures?

Cheers,
Adrian.

###############################################################################
#  Adrian Ball - Sysadmin - Adept Scientific plc, Letchworth, Herts, SG6 2HB  #

#  http://www.adeptscience.co.uk/~adrian                                      #
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