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Message-ID: <4773C3AE.1060602@mark.mielke.cc>
Date: Thu, 27 Dec 2007 10:24:30 -0500
From: Mark Mielke <mark@mark.mielke.cc>
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To: Bill Moran <wmoran@collaborativefusion.com>
CC: david@lang.hm, Florian Weimer <fw@deneb.enyo.de>,
	Fernando Hevia <fhevia@ip-tel.com.ar>,
	'pgsql-performance' <pgsql-performance@postgresql.org>
Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
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>
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	<4772CE34.2040608@mark.mielke.cc>
	<20071226171105.889f6146.wmoran@collaborativefusion.com>
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	<20071227085009.94ea3bef.wmoran@collaborativefusion.com>
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Bill Moran wrote:
> In response to Mark Mielke <mark@mark.mielke.cc>:
>
>   
>> Bill Moran wrote:
>>     
>>> I'm fairly sure that FreeBSD's GEOM does.  Of course, it couldn't be doing
>>> consistency checking at that point.
>>>       
>> According to this:
>>
>> http://www.freebsd.org/cgi/man.cgi?query=gmirror&apropos=0&sektion=8&manpath=FreeBSD+6-current&format=html
>>
>> There is a -b (balance) option that seems pretty clear that it does not 
>> read from all drives if it does not have to:
>>     
>
> >From where did you draw that conclusion?  Note that the "split" algorithm
> (which is the default) divides requests up among multiple drives.  I'm
> unclear as to how you reached a conclusion opposite of what the man page
> says -- did you test and find it not to work?
>   
Perhaps you and I are speaking slightly different languages? :-) When I 
say "does not read from all drives", I mean "it will happily read from 
any of the drives to satisfy the request, and allows some level of 
configuration as to which drive it will select. It does not need to read 
all of the drives to satisfy the request."

Cheers,
mark

-- 
Mark Mielke <mark@mielke.cc>


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Bill Moran wrote:
<blockquote
 cite="mid:20071227085009.94ea3bef.wmoran@collaborativefusion.com"
 type="cite">
  <pre wrap="">In response to Mark Mielke <a class="moz-txt-link-rfc2396E" href="mailto:mark@mark.mielke.cc">&lt;mark@mark.mielke.cc&gt;</a>:

  </pre>
  <blockquote type="cite">
    <pre wrap="">Bill Moran wrote:
    </pre>
    <blockquote type="cite">
      <pre wrap="">I'm fairly sure that FreeBSD's GEOM does.  Of course, it couldn't be doing
consistency checking at that point.
      </pre>
    </blockquote>
    <pre wrap="">According to this:

<a class="moz-txt-link-freetext" href="http://www.freebsd.org/cgi/man.cgi?query=gmirror&apropos=0&sektion=8&manpath=FreeBSD+6-current&format=html">http://www.freebsd.org/cgi/man.cgi?query=gmirror&amp;apropos=0&amp;sektion=8&amp;manpath=FreeBSD+6-current&amp;format=html</a>

There is a -b (balance) option that seems pretty clear that it does not 
read from all drives if it does not have to:
    </pre>
  </blockquote>
  <pre wrap=""><!---->
&gt;From where did you draw that conclusion?  Note that the "split" algorithm
(which is the default) divides requests up among multiple drives.  I'm
unclear as to how you reached a conclusion opposite of what the man page
says -- did you test and find it not to work?
  </pre>
</blockquote>
Perhaps you and I are speaking slightly different languages? :-) When I
say "does not read from all drives", I mean "it will happily read from
any of the drives to satisfy the request, and allows some level of
configuration as to which drive it will select. It does not need to
read all of the drives to satisfy the request."<br>
<br>
Cheers,<br>
mark<br>
<br>
<pre class="moz-signature" cols="72">-- 
Mark Mielke <a class="moz-txt-link-rfc2396E" href="mailto:mark@mielke.cc">&lt;mark@mielke.cc&gt;</a>
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