ZFS Striping and Optimizing Capabilities
ivoras at freebsd.org
Mon Apr 11 10:58:49 UTC 2011
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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