On Fri, 26 Mar 2010, Malte Schirmacher wrote:
Bob Friesenhahn wrote:
Except that ZFS does not support RAID0. I don't know why you guys
persist with these absurd claims and continue to use wrong and
misleading terminology.
What is the main difference between RAID0 and striping (what zfs really
does, i guess?)
Zfs only stripes within raidzN vdevs, and even then at the zfs record
level and not using a "RAID0" (fixed mapping on the LUN) approach.
"RAID0" and "striping" are similar concepts. When one stripes across
an array of disks, one breaks up the written block (record), and
writes parts of it across all of the disks in the stripe. This is
usually done to increase sequential read/write performance but may
also be used to assist with error recovery (which zfs does take
advantage of).
Zfs only writes whole records (e.g. 128K) to a vdev so that it does
not "stripe" across vdevs. Within a vdev, it may stripe.
The difference is pretty huge when one considers that zfs is able to
support vdevs of different sizes and topologies, as well as ones added
much more recently than when the pool was created. RAID0 and striping
can't do that.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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