another newbie question

[Brian Kelsay]

If you think this is true about the hardware RAID then you haven't seen the
Adaptec 2100 Ultra 160 RAID with dual channel and up to 128MB of standard
SDRAM.  We are testing a couple here on a server that performs backup and an
SQL server.  Fast as snot.  It's great when money is no object on a project,
"Just make it fast."  Those servers got Dual PIII-850 on one and Dual 600 on
the other in a 2U rack case, server class board, nice AGP video and Seagate
Cheetah 18 and 36GB drives.  2GB of RAM on each.  Gods, that's a lot.  The
next generation of SQL server is going to get 4GB most likely.  I know
Sprint probably has stuff to blow this away, but for us it's fast.

-----Original Message-----
From: Tony Hammitt [mailto:thammitt at kc.rr.com]
Sent: Thursday, October 19, 2000 2:37 PM
To: kclug at kclug.org
Subject: Re: another newbie question

Snip, snip

Most cards only have about 32MB of memory and maybe a 100MHz
processor to generate the checksums.  Compared with a decent PC
running 256MB of 100MHz RAM and a couple of 600MHz processors (what's
that about $800 nowadays??), the raid card doesn't have any chance of
competing.

With software raid you can also use independant controllers, possibly
on different PCI buses, which is a bit difficult to do with one card.

It is still true that spending extra money on things that you use all
of the time like faster processors and extra RAM will result in a
larger perceived performance improvement than you would get with a
raid card that you only use when doing disk I/O.  That is independant of
whether you use raid at all or how you have implemented it. 
Linux's caches work pretty well and you won't be hitting the disk all
that often except to flush the data or get something new.

The reason that the hardware raid cards exist is that they have been
around for longer and have a lot of mindshare.  Software raid is
newer and has better kernel integration but doesn't completely
invalidate hardware raid.  Some of the raid cards can store updates
and flush them out to disk in the event of a system failure.  Others
allow you to plug in many more devices than usual.

In short, hardware raid is not always faster than software raid.  You
have to allow for changes in the state of the art.  I expect that
some company will come out with a raid card with hundreds of megs of
memory and multiple processors, but most of the time you won't be
able to use this capacity for anything else.  Once you add in the
fact that most hardware raid card drivers are somewhat experimental
(due to their manufacturers being naive) it's not surprising that
people have reported software raid implementations being several
times faster than hardware.