Open Stack

On Fri, 28 Feb 2014 16:01:26 -0800
Stephen Wood <smwood4 at gmail.com> wrote:

> When originally running swift-ring-builder container.builder create, I set
> the partitions at 15 to give a total of 32768 partitions to split across 23
> hosts with 12 disks each. Now I am replacing the container service on these
> 23 hosts with 4 hosts that have 1 disk.

Are you going to re-run create, wiping all the customer data in
the cluster?

If you want to live-migrate, then you cannot change the partition
power that you selected when you stood up the cluster, and we should
not be having this conversation at all.

If you want to build everything anew, then you can use the recommended
formula from the Joe Arnold's book or a calculator like this:
 http://rackerlabs.github.io/swift-ppc/
  (currently not working in my Firefox)

For your SSD example that would be (100 * 1 * 4), rounded up is 512
or power 9. However, I would really not want to use 9, but use 15
instead. The reason is, the overhead is absolutely negligible for
powers that small, but you can't change that number over the lifetime
of the cluster. So, today you have 4 SSDs, tomorrow you have 20,
then what?

> Since I have 4 hosts with 1 disk each, do I calculate the weight of each of
> these disks as 2^15 / 4 so that the same overall partition numbers are
> available even though we're only using a handful of the disks?

Well, that sounds sane... Yes, if your original weights were about
118, then adding a big SSD with a weight of 8100 will result in
expected effect. I would still try and phase it in gradually still,
just in case if nothing else, per this:
 https://swiftstack.com/blog/2012/04/09/swift-capacity-management/

-- Pete