Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!sun-barr!decwrl!shlump.nac.dec.com!shodha.dec.com!alan
From: alan@shodha.dec.com ( Alan's Home for Wayward Notes File.)
Newsgroups: comp.sys.dec
Subject: Re: relative performance of rz23 and rz55 disks
Summary: Why the RZ23 is faster than an RZ55.
Message-ID: <454@shodha.dec.com>
Date: 20 Oct 89 18:23:29 GMT
References: <12001@watcgl.waterloo.edu>
Distribution: comp
Organization: Digital Equipment Corp. - Colorado Springs, CO.
Lines: 22

In article <12001@watcgl.waterloo.edu>, idallen@watcgl.waterloo.edu writes:
> From: "Ian! D. Allen [CGL]" <idallen>
> 
> On an 8-Meg VAXstation 3100 running Ultrix 3.0 I created a 10Meg file and
> then did:
> 
>     # time dd if=in of=out bs=1024k
> 
> The rz23 took about a minute of real time.  The rz55 consistently 
> took 10-15 seconds longer.
> Why?  

	As shipped the RZ23 has a read-ahead cache which is enabled.
	The RZ55 also has a read-ahead cache, but it isn't enabled.
	Hopefully a future version of rzdisk(8) will support turning
	on the read-ahead cache of the RZ55.  Till then, I don't
	how or even if it can be done.
	


-- 
Alan Rollow				alan@nabeth.enet.dec.com