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Date: Wed, 30 May 2007 08:29:14 +0100
From: "Peter Childs" <peterachilds@gmail.com>
Subject: Re: setting up raid10 with more than 4 drives
Cc: pgsql-performance@postgresql.org
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On 30/05/07, david@lang.hm <david@lang.hm> wrote:
>
> On Wed, 30 May 2007, Jonah H. Harris wrote:
>
> > On 5/29/07, Luke Lonergan <llonergan@greenplum.com> wrote:
> >>  AFAIK you can't RAID1 more than two drives, so the above doesn't make
> >>  sense
> >>  to me.
> >
> > Yeah, I've never seen a way to RAID-1 more than 2 drives either.  It
> > would have to be his first one:
> >
> > D1 + D2 = MD0 (RAID 1)
> > D3 + D4 = MD1 ...
> > D5 + D6 = MD2 ...
> > MD0 + MD1 + MD2 = MDF (RAID 0)
> >
>
> I don't know what the failure mode ends up being, but on linux I had no
> problems creating what appears to be a massively redundant (but small)
> array
>
> md0 : active raid1 sdo1[10](S) sdn1[8] sdm1[7] sdl1[6] sdk1[5] sdj1[4]
> sdi1[3] sdh1[2] sdg1[9] sdf1[1] sde1[11](S) sdd1[0]
>        896 blocks [10/10] [UUUUUUUUUU]
>
> David Lang
>
>
Good point, also if you had Raid 1 with 3 drives with some bit errors at
least you can take a vote on whats right. Where as if you only have 2 and
they disagree how do you know which is right other than pick one and hope...
But whatever it will be slower to keep in sync on a heavy write system.

Peter.

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<br><br><div><span class="gmail_quote">On 30/05/07, <b class="gmail_sendername"><a href="mailto:david@lang.hm">david@lang.hm</a></b> &lt;<a href="mailto:david@lang.hm">david@lang.hm</a>&gt; wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
On Wed, 30 May 2007, Jonah H. Harris wrote:<br><br>&gt; On 5/29/07, Luke Lonergan &lt;<a href="mailto:llonergan@greenplum.com">llonergan@greenplum.com</a>&gt; wrote:<br>&gt;&gt;&nbsp;&nbsp;AFAIK you can&#39;t RAID1 more than two drives, so the above doesn&#39;t make
<br>&gt;&gt;&nbsp;&nbsp;sense<br>&gt;&gt;&nbsp;&nbsp;to me.<br>&gt;<br>&gt; Yeah, I&#39;ve never seen a way to RAID-1 more than 2 drives either.&nbsp;&nbsp;It<br>&gt; would have to be his first one:<br>&gt;<br>&gt; D1 + D2 = MD0 (RAID 1)<br>&gt; D3 + D4 = MD1 ...
<br>&gt; D5 + D6 = MD2 ...<br>&gt; MD0 + MD1 + MD2 = MDF (RAID 0)<br>&gt;<br><br>I don&#39;t know what the failure mode ends up being, but on linux I had no<br>problems creating what appears to be a massively redundant (but small) array
<br><br>md0 : active raid1 sdo1[10](S) sdn1[8] sdm1[7] sdl1[6] sdk1[5] sdj1[4] sdi1[3] sdh1[2] sdg1[9] sdf1[1] sde1[11](S) sdd1[0]<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 896 blocks [10/10] [UUUUUUUUUU]<br><br>David Lang<br><br></blockquote></div><br>
Good point, also if you had Raid 1 with 3 drives with some bit errors at least you can take a vote on whats right. Where as if you only have 2 and they disagree how do you know which is right other than pick one and hope... But whatever it will be slower to keep in sync on a heavy write system.
<br><br>Peter.<br>

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