From: PFC <lists@peufeu.com>
To: Luke Lonergan <llonergan@greenplum.com>
To: Jeffrey W. Baker <jwbaker@acm.org>
To: pgsql-performance@postgresql.org
Subject: Re: Huge Data sets, simple queries
Date: Wed, 01 Feb 2006 00:11:05 +0100
Message-ID: <op.s39morhucigqcu@apollo13> (raw)
In-Reply-To: <C0050CCE.1B604%llonergan@greenplum.com>
References: <C0050CCE.1B604%llonergan@greenplum.com>
>> Linux does balanced reads on software
>> mirrors. I'm not sure why you think this can't improve bandwidth. It
>> does improve streaming bandwidth as long as the platter STR is more than
>> the bus STR.
>
> ... Prove it.
>
(I have a software RAID1 on this desktop machine)
It's a lot faster than a single disk for random reads when more than 1
thread hits the disk, because it distributes reads to both disks. Thus,
applications start faster, and the machine is more reactive even when the
disk is thrashing. Cron starting a "updatedb" is less painful. It's cool
for desktop use (and of course it's more reliable).
However large reads (dd-style) are just the same speed as 1 drive. I
guess you'd need a humongous readahead in order to read from both disks.
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To: pgsql-performance@postgresql.org
Cc: lists@peufeu.com, llonergan@greenplum.com, jwbaker@acm.org
Subject: Re: Huge Data sets, simple queries
In-Reply-To: <op.s39morhucigqcu@apollo13>
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