From: Aidan Van Dyk <aidan@highrise.ca>
To: david@lang.hm
Cc: Ron Mayer <rm_pg@cheapcomplexdevices.com>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Greg Smith <greg@2ndquadrant.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: SSD + RAID
Date: Tue, 23 Feb 2010 15:34:35 -0500
Message-ID: <20100223203435.GV14128@oak.highrise.ca> (raw)
In-Reply-To: <alpine.DEB.2.00.1002231131300.5131@asgard.lang.hm>
References: <201002221437.o1MEbDJ13005@momjian.us>
<4B82C642.8020409@cheapcomplexdevices.com>
<alpine.DEB.2.00.1002230022110.27818@asgard.lang.hm>
<alpine.DEB.2.00.1002231131300.5131@asgard.lang.hm>
* david@lang.hm <david@lang.hm> [100223 15:05]:
> However, one thing that you do not get protection against with software
> raid is the potential for the writes to hit some drives but not others.
> If this happens the software raid cannot know what the correct contents
> of the raid stripe are, and so you could loose everything in that stripe
> (including contents of other files that are not being modified that
> happened to be in the wrong place on the array)
That's for stripe-based raid. Mirror sets like raid-1 should give you
either the old data, or the new data, both acceptable responses since
the fsync/barreir hasn't "completed".
Or have I missed another subtle interaction?
a.
--
Aidan Van Dyk Create like a god,
aidan@highrise.ca command like a king,
http://www.highrise.ca/ work like a slave.
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To: pgsql-performance@postgresql.org
Cc: aidan@highrise.ca, david@lang.hm, rm_pg@cheapcomplexdevices.com, bruce@momjian.us, greg@2ndquadrant.com
Subject: Re: SSD + RAID
In-Reply-To: <20100223203435.GV14128@oak.highrise.ca>
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