On Tue, 16 Feb 2010, Dave Pooser wrote:
If I go to 10x 2TB in a RAIDZ3, will the extra spindles increase
speed, or will the extra parity writes reduce speed, or will the two factors
offset and leave things a wash?
I should mention that the usage of this system is as storage for large
(5-300GB) video files, so what's most important is sequential write speed.
With 10 disks, I would go for two raidz2 vdevs of 5 disks each. This
is not as space efficient as your one raidz3 vdev with 10 disks but it
is also likely to be a bit more responsive, and withstand a
(temporary) slowdown due to a single slow disk a bit better. With a
single raidz3 vdev, write performance will go into the toilet if even
one disk becomes a bit balky. Resilver times when a disk is replaced
are also likely to be longer.
Disks are far more likely to fail than the controller they are
attached to, and disk failures are often slow to occur, or not obvious
as failures without close scrutiny with tools like 'iostat -x'.
There have been many reports here about raidz-based pools which became
very slow, with the eventual finding that the slowness was due to just
one balky disk. I think that this is what you need to prepare for,
particularly with hardware going out on a truck to the field.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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