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From: mmengel@cuuxb.UUCP
Newsgroups: comp.sys.att
Subject: Re: 3B2 tape to tape copy
Message-ID: <1369@cuuxb.ATT.COM>
Date: Wed, 28-Oct-87 14:52:17 EST
Article-I.D.: cuuxb.1369
Posted: Wed Oct 28 14:52:17 1987
Date-Received: Sat, 31-Oct-87 11:03:52 EST
References: <1590@netsys.UUCP>
Reply-To: mmengel@cuuxb.UUCP (Marc W. Mengel)
Organization: AT&T-DSD, System Engineering for Resellers, Lisle IL
Lines: 32
Keywords: Does anyone know..

In article <1590@netsys.UUCP> len@netsys.UUCP (Len Rose) writes:
>
>Hi..
>
> Something I've been trying to do for some time has me
> quite frustrated..I need to be able to copy tape to tape
> on our 3B2 system here (yes,we have two CTC's) , and have
> not been able to come up with a fast method of accomplishing
> this.
...
> dd < /dev/rSA/ctape1 > /dev/rSA/ctape2
> cp /dev/rSA/ctape1 /dev/rSA/ctape2
>
> This works fine,does not waste system resources,but is slow as hell.

Try using a large blocksize for dd, like
	dd bs=4k < /dev/rSA/ctape1 > /dev/rSA/ctape2

This way you do fewer system calls and larger reads/writes; both of which will
make a big difference in your performance.

You might also want to try a

	dd bs=4k < /dev/rSA/ctape1 | dd bs=4k > /dev/rSA/ctape2

and see if the pipe double buffers enough to let you get simultaneous
reads and writes going on the two tapes.
-- 
 Marc Mengel	

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