Subject: RE: Is there a graph somewhere of performance vs raid group
size?
> On Mon, 31 Oct 2011, Cotton, Randall wrote:
> > Just to clarify: for me, raid group size = aggregate size - that is,
> > I'll only have one raid group per aggregate.
> I'm curious about this statement. Any reason why? What exactly is it
that you are trying to accomplish?
Well, I simply don't have enough disks yet to fill up a single raid
group per node. 80 disks, 6 nodes.
> I may not have answers to rg size vs. performance, but I can tell you
that if you limit the sizes of your aggregates, performance *will*
suffer in almost every case.
Sure, no doubt, but if I can save, say, 3 or 4 disks that I can use in
any of my 6 nodes some time in the future by making my aggregate 12 or
13 disks instead of 16, and I only lose, say, 10% performance potential
by doing so, it will make sense for us.
> While you'll start seeing benefits of striping almost immediately, you
won't get real gains for a full data center until you have many, many
disks sharing the I/O load.
Right, though I understand from conventional wisdom that the gains
diminish to tiny increments past about 16 data disks per aggregate (and
your exposure to a failed disk and long reconstruction times becomes big
enough that going past 16 may not be worth it).
> The thing is, it's in the vendor's best interests to help you
configure the units in a way that they perform well and meet your needs.
Granted the vendor also wants to sell more hardware and more disks, but
it's worth working with them and getting white papers about it.
Well said. I'll go down that road, certainly.
Thanks,
Randall