Path: utzoo!attcan!uunet!lll-winken!lll-tis!mordor!joyce!ames!ll-xn!mit-eddie!rutgers!att!ihlpb!res
From: res@ihlpb.ATT.COM (Rich Strebendt)
Newsgroups: comp.sys.att
Subject: Re: tar
Summary: 3B15 Block Size limits different for different controllers
Message-ID: <8740@ihlpb.ATT.COM>
Date: 14 Sep 88 22:22:10 GMT
References: <985@lakesys.UUCP> <650@unh.UUCP>
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 32

In article <650@unh.UUCP>, pss@unh.UUCP (Paul S. Sawyer) writes:
> In article <985@lakesys.UUCP>, steven@lakesys.UUCP (Steven Goodman) writes:
> > 
> > 	I am running an AT&T 3B15 w/UNIX 2.1.2, recently been having some
> > 	problems with "tar" and would apreciate if someone could forward
> > 	me to a utility that might solve a problem.  We sometimes 
> > 	receive source tapes written in this format on BSD 4.3 machines,
> > 	"tar" like to return the error "directory checksum error"  at this
> > 	point tar bombs out.  
> > 
> The block limit on my 3B5 tape drive is 8192 bytes.  The BSD tape was
> probably written with a larger block size.  This has happened to me.
> If ATT is listening, or CDC, who make the drives, where is the limitation, and
> ARE there any workarounds? 

There are several tape controllers available for the 3B15.  The older one,
called the Intelligent Tape Controller (ITC) has a microprocessor and a
buffer memory on it that allow it to do the job of transferring data
from memory to tape with a minimum of involvement on the part of the
CC.  The buffer is 8K bytes in size -- hence the 8K limit.

A newer controller with a faster microprocessor and a larger buffer is
available (called the Accelerated Tape Controller (ATC)).  The buffer
on the ATC is 32K bytes in size and has that as its block size limit.

There is also a SCSI controller that works with tape units.  I am not
famililar with that controller or its limits, though.

Since the limits are in the hardware rather than software, I do not
know of any way around the problem.

				Rich Strebendt
				...!att!ihlpb!res