Robert Milkowski wrote:
Hello Kyle,
Wednesday, January 10, 2007, 5:33:12 PM, you wrote:
KM> Remember though that it's been mathematically figured that the
KM> disadvantages to RaidZ start to show up after 9 or 10 drives. (That's
Well, nothing like this was proved and definitely not mathematically.
It's just a common sense advise - for many users keeping raidz groups
below 9 disks should give good enough performance. However if someone
creates raidz group of 48 disks he/she probable expects also
performance and in general raid-z wouldn't offer one.
It's very possible I misstated something. :)
I thought I had read though, something like over 9 or so disks would put
mean that each FS block would be written to less than a single disk
block on each disk?
Or maybe it was that waiting to read from all drives for files less than
a FS block would suffer?
Ahhh... I can't remember what the effect were thought to be. I thought
there was some theoretical math involved though.
I do remember people advising against it though. Not just on a
performance basis, but also on a increased risk of failure basis. I
think it was just seen as a good balancing point.
-Kyle
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