From: | PFC <lists(at)peufeu(dot)com> |
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To: | "Luke Lonergan" <llonergan(at)greenplum(dot)com>, "Jeffrey W(dot) Baker" <jwbaker(at)acm(dot)org>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Huge Data sets, simple queries |
Date: | 2006-01-31 23:11:05 |
Message-ID: | op.s39morhucigqcu@apollo13 |
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Lists: | pgsql-performance |
>> 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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