From: Bill Moran <wmoran@collaborativefusion.com>
To: Mark Mielke <mark@mark.mielke.cc>
Cc: david@lang.hm, Florian Weimer <fw@deneb.enyo.de>
Cc: Fernando Hevia <fhevia@ip-tel.com.ar>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
Date: Wed, 26 Dec 2007 17:11:05 -0500
Message-ID: <20071226171105.889f6146.wmoran@collaborativefusion.com> (raw)
In-Reply-To: <4772CE34.2040608@mark.mielke.cc>
References: <0f8201c847f6$08e15090$8f01010a@iptel.com.ar>
<Pine.LNX.4.64.0712261317320.11785@asgard.lang.hm>
<87zlvxnpkl.fsf@mid.deneb.enyo.de>
<4772CA58.5050406@mark.mielke.cc>
<Pine.LNX.4.64.0712261504310.11785@asgard.lang.hm>
<4772CE34.2040608@mark.mielke.cc>
In response to Mark Mielke <mark@mark.mielke.cc>:
> david@lang.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@collaborativefusion.com
Phone: 412-422-3463x4023
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To: pgsql-performance@postgresql.org
Cc: wmoran@collaborativefusion.com, mark@mark.mielke.cc, fw@deneb.enyo.de, fhevia@ip-tel.com.ar
Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
In-Reply-To: <20071226171105.889f6146.wmoran@collaborativefusion.com>
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