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Re: setting up raid10 with more than 4 drives - Mailing list pgsql-performance

From Peter Childs
Subject Re: setting up raid10 with more than 4 drives
Date
Msg-id a2de01dd0705300029t52ceb76fx25c3ad67db0c43c0@mail.gmail.com
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In response to Re: setting up raid10 with more than 4 drives  (david@lang.hm)
Responses Re: setting up raid10 with more than 4 drives  (Stephen Frost <sfrost@snowman.net>)
Re: setting up raid10 with more than 4 drives  ("Luke Lonergan" <llonergan@greenplum.com>)
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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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