Date: Wed, 18 Oct 2000 17:23:06 -0700 (PDT) From: Matt Dillon <dillon@earth.backplane.com> To: Mike Hoskins <mike@adept.org> Cc: Danny Braniss <danny@cs.huji.ac.il>, Gerhard Sittig <Gerhard.Sittig@gmx.net>, freebsd-stable@FreeBSD.ORG Subject: Re: PERC2 RAID support in 4.1-STABLE Message-ID: <200010190023.e9J0N6e90640@earth.backplane.com> References: <Pine.BSF.4.21.0010181500180.1382-100000@snafu.adept.org>
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:If memory serves, this is what I ordered on a couple of my new
:2450's... The 100MHz i960RX with 128MB cache. I'm planning to run some
:tests in RAID 1 and 10 modes.
:
:I'm not sure I fully understand why a lot of people are so caught up on
:RAID 5. RAID 1 seems fast and reliable given a decent controller with
:good recovery options, and RAID 10 sounds like a better solution with a
:larger quantity of drives.
A mirrored setup (RAID-1) will be a whole lot faster then a parity
setup (RAID-5), since different read requests can be dispatched to
both sides of the mirror simultaniously and writing does not require
parity calculation.
The difference between the two is cost. If you are building a
100GB partition out of 25GB hard drives, a mirrored configuration
will require 8 drives (100GB x 2 for the mirror), whereas a parity
configuration will require only 5 drives.
So what you need to do is calculate how much disk space you need,
what kind of load you intend to place on the RAID array, and then
figure out the cost/performance tradeoff that best suits you. Then
pick either mirroring or raid based on that.
Mirrored setups are especially good in systems which need to seek
around a lot. A year or so ago I added seek zones to the CCD device
(though I will stress that CCD implements only a poor-man's mirroring
system and is no where near as sophisticated as VINUM or a real
raid controller). If you 'man ccd' you will get a pretty detailed
description of your options in regards to CCD and VINUM.
-Matt
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