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Message-ID: <37617756.14E1EAF2@vinschen.de>
Date: Fri, 11 Jun 1999 22:53:42 +0200
From: Corinna Vinschen <corinna AT vinschen DOT de>
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To: Jim & Jenn Dumser <dumser AT bigfoot DOT com>
CC: cygwin AT sourceware DOT cygnus DOT com
Subject: Re: cygwin tar to tape?
References: <s7318bc6 DOT 078 AT experian DOT com> <3731B674 DOT 63588B38 AT cityweb DOT de> <375E670E DOT 84E188E8 AT ericsson DOT com>
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James Dumser wrote:
> 
> I've been experimenting with tape support under WinNT with your
> "unofficial" cygwin1.dll. I tarred up some files on a Sun Ultra (running
> Solaris), but when I tried to read it under cygwin, I get "permission
> denied." I also tried the other way: create a tape under cygwin and read

You get this `permission denied' when you try to read a tape, that is
written with another blocking factor than the Windows tape driver is set to.
Windows has no automatical recognition for this!!!

You must(!) know the blocking (U*Xes typically uses 5K blocking) and
you have to set it with my `mt' command from ftp site

ftp://ftp.franken.de/pub/win32/develop/gnuwin32/cygwin/porters/Vinschen_Corinna/B20

to set blocksize to e.g. 5K:

	mt setblk 5120

> it on the Ultra. (I'm using GNU tar on both machines.) When I do this,
> tar (on the Ultra) reports a blocking factor of 1 (even though I
> specified a blocking factor of 100 when wrote the tape), and reading is
> incredibly slow.

The default blocksize under NT is 512 Bytes. It's a `feature' of Windows.
Use my `mt' command from ftp site

ftp://ftp.franken.de/pub/win32/develop/gnuwin32/cygwin/porters/Vinschen_Corinna/B20

to set blocksize to e.g. 5K once:

	mt setblk 5120

But be warned! Another `oh so wunderful feature' of Windows is, that
you only may set blocksize, if a tape is in the drive!!!

You may also use my patched `tar' from the same site. This tar sets the
blocksize by itself to a default of 10K unless you use the -b option
to set your own blocksize.

Same convenience with patched `cpio' from the same site, which sets blocksize
to e.g. 5K if you use the -B option.

Another hint:
All this only has an effect, if the tape driver supports setting blocksize!
I know it works for the DDS driver which is part of NT 4.0 distribution.
Older tape drives may use fixed blocksizes.

Regards,
Corinna

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