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Date: Sun, 8 Jun 2008 18:33:15 -0500
From: Dan Nelson <dnelson@allantgroup.com>
To: Ivan Voras <ivoras@freebsd.org>
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X-OS: FreeBSD 7.0-STABLE
User-Agent: Mutt/1.5.18 (2008-05-17)
Cc: freebsd-questions@freebsd.org
Subject: Re: FreeBSD + ZFS on a production server?
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In the last episode (Jun 09), Ivan Voras said:
> Wojciech Puchar wrote:
> > 2) ZFS RAID-z turns your X drives to single drive performance both
> > on read and write. every normal RAID-5 implementation will give you
> > random read speed of X-1 times single drive speed, while slow
> > random write speeds (but still at least half of single drive). but
> > this is advertised as a feature
> 
> Is this because of checksum verification (the need to read all
> components) or something else? Any documentation/references?

RAID-Z stores a single checksum over the whole stripe, instead of
checksumming each disks's section separately, so it has to read from
all disks to validate the stripe.  Only random reads are penalized,
though.

http://blogs.sun.com/roch/entry/when_to_and_not_to

-- 
	Dan Nelson
	dnelson@allantgroup.com