I’m trying to set up an erasure coded pool with k=9 m=6 on 13 osd hosts. I’m
trying to write a crush rule for this which will balance this between hosts as
much as possible. I understand that having 9+6=15 > 13, I will need to parse
the tree twice in order to find enough pgs. So what I’m trying to do is select
~1 from each host on the first pass, and then select n more osds to fill it
out, without using any osds from the first pass, and preferably balancing them
between racks.
For starters, I don't know if this is even possible or if its the right
approach to what I'm trying to do, but heres my attempt:
rule .us-phx.rgw.buckets.ec {
ruleset 1
type erasure
min_size 3
max_size 20
step set_chooseleaf_tries 5
step take default
step chooseleaf indep 0 type host
step emit
step take default
step chooseleaf indep 0 type rack
step emit
}
This gets me pretty close, the first pass works great and the second pass does
a nice balance between racks, but in my testing ~ 6 out of 1000 pgs will have
two osds in their group. I'm guessing I need to get down to one pass to make
sure that doesn't happen, but I'm having a hard time sorting out how to hit the
requirement of balancing among hosts *and* allowing for more than one osd per
host.
Thanks, Aaron
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