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From: kenh@techbook.com (Ken Haynes)
Newsgroups: comp.sys.novell
Subject: Re: Disk duplexing: 3.0/3.1, Adaptec 1540, external SCSI
Keywords: duplexing, SCSI, Novell
Message-ID: <1990Dec26.151001.21431@techbook.com>
Date: 26 Dec 90 15:10:01 GMT
References: <1990Dec21.234852.21220@momenta>
Distribution: na
Organization: TECHbooks of Beaverton Oregon - Public Access Unix
Lines: 87

In article <1990Dec21.234852.21220@momenta> gregpf@momenta (Greg Presedo-Floyd) writes:
>I have questions on "Disk duplexing".
>
>0) Our server environment:
>
>   We have Adaptec 1540 SCSI boards.  They drive Fujitsu 1 Gig external
>   winchesters. 
>
>   Netware 386 3.0 (moving to 3.1) .  Ethernet NE2000 and WD8003 coax and
>   10BaseT cards.

Make sure that you have backed up all your data *before* you upgrade.  The
migration path to 3.1 using the generic SCSI driver NLM requires that you
repartition the drive.  This will cause all data to be lost! If you got the
3.0 generic SCSI fix, you've already done this.... assuming you've installed
the fix.

>
>1) What is "disk duplexing" ?:
>
>      "Disk duplexing" , as I understand it, allows an entire SCSI chain
>      (disk controller, all disk(s) connected to that controller) to be
>      continuously and transparently have the same data written to each
>      redundant side.

Correct.

>
>      If something on one side goes bad, operations continue and the OS
>      sends a warning message out.
>
>      I think I need to go to an Adaptec re-seller and get a Netware
>      "disk duplex" NLM to do this.

Nope.  You only need another disk controller card and drive to duplex. You
set up the duplexing you would use the install.nlm program.  Refer to the 
installation manual under load INSTALL pg. 131 of NW3.1 Installation.

>
>2) QUESTIONS about "duplexing" :
>
>      Is my specific hardware "duplex-able" ?

It should be.

>      Will this work ?  Is it working at your site ? 

It does work.  It is working at my site, although not in exactly the same
configuration.

>      How hard was it for you to set up ?

Piece of cake.

>      Has anyone had a disk/controller failure and had this save them ?

Yep. Although not since we've upgraded to NW386.  It did save me on a 2.15
SFT system.

>      A supplimentary thing that I will do to make our server operations 
>      robust is to have an identical second server, also disk duplexed,
>      operating and on-line or at least powered down and standing by.

Server duplexing is not far away.  Until you can mirror servers, what you 
are doing is the best bet.

>
>      Will these 2 things make my server as robust as possible ?
>      More suggestons ?
>

Not only will it make your server more robust, it will increase performance
as well.  NW386 will assign read/write operations as efficiently as possible
performing what is called a "split seek", or getting the data from both
disks at the same time but different parts of the file. In other words,
it will schedule disk 1 to get sectors 1, 3, 5, and 7 while it schedules
disk 2 to get sectors 2, 4, 6, and 8.  This decreases head seek time and 
thus increases performance.


Good luck!
Ken
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