Date: Sun, 15 Mar 1998 18:44:53 -0600 From: Raul Zighelboim <rzig@gulfsouth.verio.net> To: "'shimon@simon-shapiro.org'" <shimon@simon-shapiro.org> Cc: "scsi@freebsd.org" <scsi@FreeBSD.ORG> Subject: RE: to raid or not to raid Message-ID: <A03CD00C69B1D01195AB00A024ECEB167110DC@kaori.communique.net>
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My missing link is:
Will a (7 drive array under raid 5) be faster than a sinlg larger drive
?...
Will it be as fast as a (5 drive raid 5 array) ?
Thanks.
> -----Original Message-----
> From: Simon Shapiro [SMTP:shimon@simon-shapiro.org]
> Sent: Sunday, March 15, 1998 12:07 PM
> To: Raul Zighelboim
> Cc: scsi@freebsd.org
> Subject: RE: to raid or not to raid
>
>
> 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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