Hi Kyle,
I think there was a lot of talk about this behavior on the RAIDZ2 vs.
RAID-10 thread. My understanding from that discussion was that every
write stripes the block across all disks on a RAIDZ/Z2 group, thereby
making writing the group no faster than writing to a single disk.
However reads are much faster, as all the disk are activated in the
read process.
The default config on the X4500 we received recently was RAIDZ-groups
of 6 disks (across the 6 controllers) striped together into one large
zpool.
Best Regards,
Jason
On 1/10/07, Kyle McDonald <[EMAIL PROTECTED]> wrote:
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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