Hi,
I have questions about the "stretch mode" feature [1].
1) In the limitations section [2] it is stated that EC pools support
is not implemented yet. Does anyone know what things are missing? I
understand that there should be a restriction on K+M values, I suppose
only profiles with M >= K+2 should be allowed so we would have at
least K+1 shards on every site. And for 2+4 profile the rule could be:
rule stretch_rule {
id 1
type replicated
step take site1
step chooseleaf indep 3 type host
step emit
step take site2
step chooseleaf indep 3 type host
step emit
}
This is based on the example for a replicated pool provided in the
stretch mode documentation.
And I just tried, and to make it (apparently) work I just had to
remove the EC pool restrictions in the code. So I wonder what I am
missing.
2) Looking at the example for a replicated pool in the doc [1] (which
I used to make a rule for replicated pool):
rule stretch_rule {
id 1
type replicated
step take site1
step chooseleaf firstn 2 type host
step emit
step take site2
step chooseleaf firstn 2 type host
step emit
}
With this rule the primary is alway on the site1 (and the same problem
is with my ec rule BTW), which does not look like perfect, i.e. the
reads will always go to osds on site1. Is it a known limitation?
[1] https://docs.ceph.com/en/latest/rados/operations/stretch-mode/
[2] https://docs.ceph.com/en/latest/rados/operations/stretch-mode/#stretch-mode-limitations
--
Mykola Golub
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