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Date:      Mon, 11 Apr 2011 12:58:33 +0200
From:      Ivan Voras <ivoras@freebsd.org>
To:        freebsd-questions@freebsd.org
Subject:   Re: ZFS Striping and Optimizing Capabilities
Message-ID:  <inumsp$d9b$1@dough.gmane.org>
In-Reply-To: <4DA131BD.3030805@telting.org>
References:  <4DA131BD.3030805@telting.org>

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On 10/04/2011 06:27, Chris Telting wrote:
> Just a few questions about what ZFS actually does. So if anyone has
> intimate knowledge about ZFS's implementation on Freebsd I'm sure I and
> others would appreciate the answers.
>
> When you add a second and or thrid drive/partition to a zpool I'm
> assuming that it's going to start using the drives like a raid 0 stripe.

Not exactly like RAID 0; ZFS's "striping" is not using regular patterns 
/ stripes but "IO balancing" heuristics. This means there are no fixed 
stripe size but the data is distributed across the drives in a way which 
ZFS's algorithms predict is best.

This allows for e.g. creating a zpool from a single drive, then adding 
another drive (as a "stripe") and ZFS will use both, but new data will 
be written mostly to the new drive. Performance should scale as expected 
in this scenario, e.g. not much if the first drive is almost full before 
adding a new one.





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