I asked as well, it seems nobody on the list knows so far.
On 9/30/21 10:34 AM, Andrew Gunnerson wrote:
Hello,
I'm trying to figure out what overlapping roots entails with the default
scale-down autoscaling profile in Ceph Pacific. My test setup involves a CRUSH
map that looks like:
ID=-1 | root=default
ID=-58 | rack=rack1
ID=-70 | host=ssd-1
| <OSDs>
ID=-61 | rack=rack2
ID=-55 | host=ssd-2
| <OSDs>
ID=-62 | rack=rack3
ID=-52 | host=ssd-3
| <OSDs>
ID=-63 | rack=rack4
ID=-19 | host=hdd-1
| <OSDs>
| <15 more hosts>
The CRUSH rules I created are:
# Rack failure domain for SSDs
ceph osd crush rule create-replicated replicated_ssd default rack ssd
# Host failure domain for HDDs
ceph osd crush rule create-replicated replicated_hdd default host hdd
ceph osd erasure-code-profile set erasure_hdd ruleset k=3 m=2 crush-device-class=hdd crush-failure-domain=host
and the pools are:
Pool | CRUSH rule/profile | Overlapped roots error
---------------------------|--------------------|-----------------------
device_health_metrics | replicated_rule | -1 (root=default)
cephfs_metadata | replicated_ssd | -51 (root=default~ssd)
cephfs_data_replicated_ssd | replicated_ssd | -51 (root=default~ssd)
cephfs_data_replicated_hdd | replicated_hdd | -2 (root=default~hdd)
cephfs_data_erasure_hdd | erasure_hdd | -1 (root=default)
With this setup, the autoscaler is getting disabled in every pool with the
following error:
[pg_autoscaler WARNING root] pool <num> contains an overlapping root -<id>... skipping scaling
There doesn't seem to be much documentation about overlapped roots. I think I'm
fundamentally not understanding what it means. Does it mean that the autoscaler
can't handle two different pools using OSDs under the same (shadow?) root in the
CRUSH map?
Is this setup something that's not possible using the scale-down autoscaler
profile? It seems that the scale-up profile doesn't have a concept of overlapped
roots.
Thank you,
Andrew
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