Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!husc6!mit-eddie!apollo!weber_w
From: weber_w@apollo.COM (Walt Weber)
Newsgroups: comp.sys.apollo
Subject: Re: TAR (SR9.X), cartridges
Message-ID: <431a057f.10b48@apollo.COM>
Date: 8 May 89 16:43:00 GMT
References: <503@zgdvda.UUCP>
Reply-To: weber_w@apollo.COM (Walt Weber)
Organization: Apollo Computer, Chelmsford, MA
Lines: 46

In article <503@zgdvda.UUCP> pfuetzner@zgdvda.UUCP (Matthias Pfuetzner) writes:
>I've got a question concerning TAR under SR9.2 and SR9.7:
>1.) Why is the device for the cartridge tape
>   /dev/rmt/c0d0h
>and not 
>   /dev/rctX .....

Both are present, assuming that the installation of Domain/IX was done by
our installation tools.  It sounds like you are accessing the SysV device
special file and not the BSD.  You should be able to use /com/edmtdesc to
look at c0d0h and create a duplicate as /dev/rct8 or /dev/rct12.  But I'm
suspicious about how the BSD device entries got deleted, and wonder what
else might be missing from your system.

>2.) Is there any possibility to TAR to tape WITHOUT doing a
>   rbak -dev ct -rewind
>before each
>   tar f /dev/rmt/c0d0h ?
>(Without the rbak command I always get the message:
>tar: cannot open /dev/rmt/c0d0h !!)

Last time I looked (more than 8 months ago) the -rewind was only necessary
when a ctape is inserted in the drive; are you changing tapes?

>3.) Is there any possibility to SPEEDUP cartridge tape actions?
>Writing about 8 Mbyte to cartridge tape on a standard Sun 3/60 takes 
>about 8 minutes (/dev/rst8), reading them bak with tar on an APOLLO
>(DN 3000, DN 580) takes about 90 minutes (no jobs on the machine, no 
>jobs on the network!!)

Conventional wisdom (a.k.a. "folklore") is that writing to disk will always
take longer than reading, since new files need to have space "found" for
them, rather than chasing pointers to existing blocks as in the read operation.
An increase of slightly over 11x "feels wrong", and since we (as users) always
want it faster, less expensive, and available now, can you tell me how long
it takes to WRITE that same 8Mb to disk (under a new pathname) on your 3/60?
And how long does it take us to write those files from the DN3000 to ctape?
( No sense fixing one tire if we've got two flats :-)

>   Matthias Pfuetzner

...walt...
-- 
Walt Weber                            Apollo Computer          
(508) 256-6600 x8315                  People's Republic of Massachusetts
-The views expressed herein are personal, and not binding on Apollo-