From: Mark Mielke <mark@mark.mielke.cc>
To: Bill Moran <wmoran@collaborativefusion.com>
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 17:21:14 -0500
Message-ID: <4772D3DA.10302@mark.mielke.cc> (raw)
In-Reply-To: <20071226171105.889f6146.wmoran@collaborativefusion.com>
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>
<20071226171105.889f6146.wmoran@collaborativefusion.com>
Bill Moran wrote:
>
>> 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.
>
According to this:
http://www.freebsd.org/cgi/man.cgi?query=gmirror&apropos=0&sektion=8&manpath=FreeBSD+6-c...
There is a -b (balance) option that seems pretty clear that it does not
read from all drives if it does not have to:
Create a mirror.
The order of components is important,
because a component's priority is based on its position
(starting from 0). The component with the biggest priority
is used by the prefer balance algorithm and is also used as a
master component when resynchronization is needed, e.g. after
a power failure when the device was open for writing.
Additional options include:
*-b* /balance/ Specifies balance algorithm to use, one of:
*load* Read from the component with the
lowest load.
*prefer* Read from the component with the
biggest priority.
*round-robin* Use round-robin algorithm when
choosing component to read.
*split* Split read requests, which are big-
ger than or equal to slice size on N
pieces, where N is the number of
active components. This is the
default balance algorithm.
Cheers,
mark
--
Mark Mielke <mark@mielke.cc>
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To: pgsql-performance@postgresql.org
Cc: mark@mark.mielke.cc, wmoran@collaborativefusion.com, 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: <4772D3DA.10302@mark.mielke.cc>
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