RE: Raid 5 Vs Mirroring Performance

[Neil Palmer <npalmer@xxxxxxxxxxx>]

Standard lawyers answer - it depends.
On what ?  Well, many things, including:

# of disks on your system (basically how many disk arms do we have)
System model (performance rating)
Model of RAID-5 controller (9337-xxx, internal 6512, 6522, etc.)
        (there are many sizes of cache used for RAID-5 buffers, and the
oldest 9337 implementation used a Write Assist Drive - where data would
be dumped immediately until the controller confirmed it had written the
striped data - and no cache at all).

In general mirroring will provide better performance than RAID-5, just
like a BMW provides a nicer ride than a Ford Escort.  You have to
balance the performance with what you are willing to pay.

And of course that standard question - are you NOTICING a performance
problem with your system (is disk busy % abnormally high and is response
time suffering).
If not - then you don't have a problem to be concerned with.
(If any application would show a performance problem, it's likely to be
a batch job that does a lot of file writes/updates).

... Neil Palmer                                     AS/400~~~~~      
... NxTrend Technology - Canada     ____________          ___  ~     
... Thornhill, Ontario,  Canada     |OOOOOOOOOO| ________  o|__||=   
... Phone: (905) 731-9000  x238     |__________|_|______|_|______)   
... Cell.: (416) 565-1682  x238      oo      oo   oo  oo   OOOo=o\   
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... mailto:NPalmer@NxTrend.com          http://www.NxTrend.com


        -----Original Message-----
        From:   Jeff Wallin [SMTP:Jeff.Wallin@hbfuller.com]
        Sent:   Tuesday, February 03, 1998 3:20 PM
        To:     MIDRANGE-L@midrange.com
        Subject:        Raid 5 Vs Mirroring Performance

        We use Raid 5 on all of our AS/400's.  Recently a Unix admin
told me that we would gain a lot of performance if we would mirror our
disk drives instead.  Does anyone know how much performance we are
giving up by using RAID 5 vs mirroring....

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