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From: lp@decvax.dec.com (Larry Palmer )
Newsgroups: comp.sys.dec
Subject: Re: Strange Disk Performance Help!
Message-ID: <373@decvax.decvax.dec.com.UUCP>
Date: 18 Sep 90 14:14:41 GMT
References: <15500017@hpdmd48.boi.hp.com>
Sender: news@decvax.dec.com.UUCP
Lines: 25

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The difference in performance (dec RZ55 vs other disks) comes from
the enabling of a read ahead cache on the disk drive. This greatly
improves both raw and file system performance. Issue the command

        rzdisk -g current /dev/rrz?a

and page through the output. Page code 8 (cacheing parameters) on
the RZ55 will show that the read cache is enabled (on greater than
rev 700 firmware RZ55's). Some other vendors also allow read caching
to be enabled on their disks but most do NOT enable it by default.
You might try rzdisk on an unused (and unimportant) drive and
see if the drive produces anything rzdisk understand (each vendor
seems to want to put things is different format pages). The -g
option wont hurt your disk but others might so be careful.

The TRYSYNC field is probably working if it has been set and
the drive understand how to do synchronous transfers.


---   Larry Palmer		 Ultrix Networking/AD
---   Digital Equipment Corporation
---   Nashua, New Hampster
---   ... One of the fathers of PMAX ...