Eric Schrock wrote:
On Thu, Aug 03, 2006 at 10:24:12AM -0700, Marion Hakanson wrote:
zpool create mirror c0t2d0 c0t3d0 mirror c0t0d0s5 c0t1d0s5
Is this allowed? Is it stupid? Will performance be so bad/bizarre that
it should be avoided at all costs? Anybody tried it?
Yes, it's allowed, but it's definitely not an ideal solution. Unless
you manually tweak the write cache (as mentioned elsewhere, this could
be bad for other slices), you'll end up with asymmetric performance on
these two vdevs. The current ZFS allocation and I/O policies don't take
latency into account (they're based solely on capacity), and so a slower
vdev will slow down the entire pool.
Is the fact that there are more spindles in general going to help at
all? So in this case he's got a pool consisting of two mirrored stripes.
Isn't performance still going to be better than if he dropped off the
slower slices/stripe and had a single mirror? Won't the system be able
to handle more i/os in general by taking advantage of the additional
bandwidth provided by each controller?
For example, while one block is being written to the slower stripe, it
may also be able to write another block to the faster stripe concurrently?
--joe
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