From: Doggy \(tru64\) (tru64dog@yahoo.com)
Date: Fri Jul 05 2002 - 17:17:02 EDT
Original Question:
===
For my mail implementation, I have 6 disks to use; two
to mirror the OS and 3 disks with one parity disk for
redundancy. My buddy over here wants to wants to put
in a mirror set disk0 and disk1, another mirror set of
disk2 and disk3, and a final mirror set of disk4 and
disk5 -- then incorporate that all in a strip set;
giving 25% to the OS and the rest to the data. I
really don't like his way just in case the OS hoses, I
have to break the stripset in order to repair the os
mirror set with a new jbod (hardware redundancy). Do I
have a valid point? Is worth the stripping for
performance? Or I am raising a stink for nothing?
====
Many thanks to:
(if I forgot somebody, sorry)
Jerome M Berkman
Elizabeth Harvey-Forsythe
Kevin Fleming
Wheelock, Michael D
A. Mahendra Rajah
alan@ nabeth.cxo.cpqcorp.net
Below are some of the comments I recieved:
===
In the right I/O load strip[p]ing can certainly be
worth
it. A mail application might be one of those loads,
since
it will probably have multiple readers, each with
their
own I/O load. If the mail writer is single threaded
(one
incoming mail message at time), that limits the
usefulness
a little.
Both configuration have their advantages. Without
more
information as to the precise hardware and software
organization, it is hard to guess which one would be
better.
===
Most mail is relatively small - striping won't help.
Striping is really good when you have a few
applications
pounding the disk with long I/O reads or writes.
I think it just increases your vulnerability - if
one pair goes bad, you've lost everything.
Of course, I've never been able to convince anyone of
this.
On the other hand, you have 11 mirrored and not
striped pairs
in our RA7000, for our mail server, so maybe they did
listen.
===
I would definitely keep the OS seperate from your
data. I would use
two
disks as a mirror for the OS and use the remaing 4
disks as a RAID 5.
It's
a good balance of performance and redundancy and makes
a any repair or
migration job easier.
===
>From a strict hardware standpoint, software striping
shows minimal performance gains at best. Because you
are still shipping that data over a single scsi bus
(or two) you still have the largest bottleneck which
is bus contention. Typically striping works best with
a hardware solution such as an hsz or hsg series
controller. These have six scsi busses each and the
I/O can be spread across all of them
===
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