Date: Sun, 15 Mar 1998 10:07:13 -0800 (PST) From: Simon Shapiro <shimon@simon-shapiro.org> To: Raul Zighelboim <rzig@gulfsouth.verio.net> Cc: "scsi@freebsd.org" <scsi@FreeBSD.ORG> Subject: RE: to raid or not to raid Message-ID: <XFMail.980315100713.shimon@simon-shapiro.org> In-Reply-To: <A03CD00C69B1D01195AB00A024ECEB167110D9@kaori.communique.net>
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On 15-Mar-98 Raul Zighelboim wrote:
> Hello there;
>
> Could anyone point me to documentation on the pros and cons of raid
> 5/raid 0 in a non-pro language ?
> Also, any pro/cons off 'raid 0 over raid 5' ?
Apples and Oranges. RAID-0 is not RAID at all. It is simply striping.
RAID-5 uses a scheme where each driver contains some data and some
``disaster recovery information'';
RAID-0 is good for speed. The more disks, the faster things go.
RAID-5 is god for data reliabiliy; if ONE driver fails, the data is still
all there and can be recovered.
RAID-0 is unreliable; as you add drives, your MTBF (Mean Time Between
Failures) goes down. If you loose one drive, you loose ALL the data.
RAID-5 is slow; Data has to be recorded in more than one place. RAID =-5
is very slow if degraded (one drive failed); every sector off the dead
drive has to be computed for the rest of the drives.
RAID-0 is economical; You get to use ALL the capacity you give it. You
can have as small an array as 2 drives, or as large as you have drives
(almost).
RAID-5 is wasteful; You always loose one drive worth of storage capacity.
RAID-5 does not scale well. A RAID-5 array with 100 drives is not as fast
as one with 5 drives.
> What I mean by that is to ccd multiple raid 5 arrays to do load
> balancing over multiple scsi busses.
This is one method of acomplishing it. Another method to achive balance
over multiple SCSI busses, is using a DPT PM33334 type controller. It
allows you to have RAID-{0,1,5} striped across three busses, totally
transparent to the O/S; You can then install any number of O/S's, all
sharing in the same RAID arrays. You can then take multiple controllers
and create a CCD RAID-0 across the controllers.
----------
Sincerely Yours,
Simon Shapiro
Shimon@Simon-Shapiro.ORG Voice: 503.799.2313
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