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From: josh@polaris.UUCP (Josh Knight)
Newsgroups: net.unix-wizards
Subject: Re: need help with multi-reel cpio
Message-ID: <544@polaris.UUCP>
Date: Mon, 26-May-86 02:30:59 EDT
Article-I.D.: polaris.544
Posted: Mon May 26 02:30:59 1986
Date-Received: Tue, 27-May-86 00:31:25 EDT
References: <520@sdcc13.UUCP> <461@ncr-sd.UUCP> <529@isis.UUCP> <862@uqcspe.OZ> <888@ncr-sd.UUCP>
Reply-To: josh@polaris.UUCP (Josh Knight)
Organization: IBM Research, Yorktown Heights, N.Y.
Lines: 44
Keywords: cpio tape backup
Summary: Make it easy to make reels that can be copied

In article <888@ncr-sd.UUCP> greg@ncr-sd.UUCP (Greg Noel) writes:
>In article <862@uqcspe.OZ> tony@uqcspe.UUCP writes:
...
...
...
>>	The doc follows :-
>>
>> .....  [ A description of a program that handles multiple-volume files.
>>        Volume overflow on output is detected by pre-specifying how many
>>        blocks can be made to fit on the volume.  Specificly: ]
>>
>>     .............   If  the  device  or  its
>>     driver  does not allow successful writing all the way to the
>>     end of a physical volume, such as with magnetic tape, the -n
>>     count  options  should be used to specify the maximum number
>>     of physical blocks to be written on one volume.
>
>Aye, here's the rub -- all of the volumes must be at least this size.  In a
>normal computer center, tapes are routinely shortened when a bad spot occurs
>near the beginning.  Since these are the tapes you are likely to get when an
>operator is doing your backups, you can't expect that some number of blocks
>will fit on a tape volume unless you routinely waste several hundred feet on
>every volume.  It is just the sort of restriction described in the paragraph
>above that I wish to see eradicated.

Yes, but unless all you are making is back-up tapes that no one else
wants to look at and that will be obsolete in a few weeks, don't take
out the feature that allows one to copy the tapes.  For the reasons
Greg cited plus the usual variance in tape lengths as they come from
the manufacturer and variations in the size of interrecord gaps as
written by different individual devices, if you want to be able
to make copies of these multi-reel collections, writing a number
of blocks that you are SURE will fit on one tape reel is very good
idea.  A generalized multi-reel tape handling facility should have
it.  I don't think it should be in the driver, but the filter that
was offerred sounds like just where it belongs.

Of course, any opinions, expressed or implied are mine and not my
employers.

-- 

	Josh Knight, IBM T.J. Watson Research
 josh@ibm.com, josh@yktvmh.bitnet,  ...!philabs!polaris!josh