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Date:      Sat, 16 Jul 2005 11:15:38 -0400
From:      Chuck Swiger <cswiger@mac.com>
To:        Nikolas Britton <nikolas.britton@gmail.com>
Cc:        FreeBSD - Questions <freebsd-questions@freebsd.org>
Subject:   Re: RAID Level 55
Message-ID:  <42D9249A.2050007@mac.com>
In-Reply-To: <ef10de9a0507160019499517ab@mail.gmail.com>
References:  <ef10de9a0507160019499517ab@mail.gmail.com>

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Nikolas Britton wrote:
> I was reading on wikipedia about RAIDs trying to pass the time and I
> was thinking why not have RAID 5+5 or 5+5+5 levels, sure you waste
> 2/3th's of your space but wouldn't this be a killer setup for a
> directory server where fast reads are of the utmost importance?

Actually, no.  RAID-5 prioritizes cost and reliability at the expense of 
performance.  RAID-5 does adequate for read-mostly volumes with big files, and 
does worst with lots of writes to small files.

RAID-5,0 or -1,0 would be a much better choice.

> Would you add up the transfer rates for each drive to get the total
> transfer rate of the array?, if true you could easily saturate a 10
> gigabit ethernet connection with a 555 array of IDE or SATA drives.

Nope.  Most machines are limited by their PCI bus and chipset to less than 
1Gb/s of backplace bandwidth, although the higher-end boxes with multiple PCI 
busses or PCIe will do better.

-- 
-Chuck



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