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From: grr@cbmvax.commodore.com (George Robbins)
Newsgroups: comp.unix.wizards
Subject: Re: Finding tape block size
Message-ID: <19041@cbmvax.commodore.com>
Date: 16 Feb 91 05:17:06 GMT
References: <1991Feb12.224353.6514@gjetor.geac.COM>
Reply-To: grr@cbmvax.commodore.com (George Robbins)
Organization: Commodore, West Chester, PA
Lines: 22

In article <1991Feb12.224353.6514@gjetor.geac.COM> adeboer@gjetor.geac.COM (Anthony DeBoer) writes:
> I periodically get tapes from client's systems or other sources where the
> precise tape format isn't documented.  What I'm looking to find out is if
> there's a way to determine exactly what block size was used when the tape was
> written, or even if this is a major requirement (should I even be worrying
> about it or not?).  Reading with a tasteful default value usually seems to
> work (even a 512-byte block size has worked before, although at tremendous
> loss of efficiency), but I'm wondering if there's any chance of data loss with
> the wrong block size, or any rule of thumb for optimizing things.

dd if=/dev/nrmt* of=diskfile bs=65535 count=1 ; ls -l diskfile ...
	- or -
dd if=/dev/nrmt* bs=65535 count=1 | wc -c

Different tape devices have different characteristics.  A sun type cartridge
tape is insensitive to blocksize (except as a performance issue), traditional
raw 9-track tapes may well lose data...

-- 
George Robbins - now working for,     uucp:   {uunet|pyramid|rutgers}!cbmvax!grr
but no way officially representing:   domain: grr@cbmvax.commodore.com
Commodore, Engineering Department     phone:  215-431-9349 (only by moonlite)