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Re: With 4 disks should I go for RAID 5 or RAID 10

From: Bill Moran <wmoran(at)collaborativefusion(dot)com>
To: Mark Mielke <mark(at)mark(dot)mielke(dot)cc>
Cc: david(at)lang(dot)hm, Florian Weimer <fw(at)deneb(dot)enyo(dot)de>, Fernando Hevia <fhevia(at)ip-tel(dot)com(dot)ar>, 'pgsql-performance' <pgsql-performance(at)postgresql(dot)org>
Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
Date: 2007-12-26 22:11:05
Message-ID: 20071226171105.889f6146.wmoran@collaborativefusion.com (view raw or flat)
Thread:
Lists: pgsql-performance
In response to Mark Mielke <mark(at)mark(dot)mielke(dot)cc>:

> david(at)lang(dot)hm wrote:
> > On Wed, 26 Dec 2007, Mark Mielke wrote:
> >
> >> Florian Weimer wrote:
> >>>> seek/read/calculate/seek/write since the drive moves on after the
> >>>> read), when you read you must read _all_ drives in the set to check
> >>>> the data integrity.
> >>> I don't know of any RAID implementation that performs consistency
> >>> checking on each read operation. 8-(
> >> Dave had too much egg nog... :-)
> >> Yep - checking consistency on read would eliminate the performance 
> >> benefits of RAID under any redundant configuration.
> > except for raid0, raid is primarily a reliability benifit, any 
> > performance benifit is incidental, not the primary purpose.
> > that said, I have heard of raid1 setups where it only reads off of one 
> > of the drives, but I have not heard of higher raid levels doing so.
> What do you mean "heard of"? Which raid system do you know of that reads 
> all drives for RAID 1?

I'm fairly sure that FreeBSD's GEOM does.  Of course, it couldn't be doing
consistency checking at that point.

-- 
Bill Moran
Collaborative Fusion Inc.
http://people.collaborativefusion.com/~wmoran/

wmoran(at)collaborativefusion(dot)com
Phone: 412-422-3463x4023

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Next:From: Bill MoranDate: 2007-12-26 22:16:08
Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
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