Hi, I couldn't find any newer information than this:
PG merging works similarly to splitting, except that internally the pg_num value is always decreased a single PG at a time. Merging is a more complicated and delicate process that requires IO to the PG to be paused for a few seconds, and doing merges a single PG at a time allows the system to both minimize the impact and simplify the overall complexity of the process.
https://ceph.io/en/news/blog/2019/new-in-nautilus-pg-merging-and-autotuning/ Regards, Eugen Zitat von Justin Mammarella <justin.mammarella@unimelb.edu.au>:
Hi folks,
We are in the process of shrinking a CEPH cluster from around 2000 osds to 300 osds.
We need to reduce our pg count from 16384 to 8192.
After setting pg_num to 8192, it’s currently it’s taking 3 hours to reduce the pool’s PG count by one. Which given the number of PGs, will take over 2 years to complete.
Are there any tunables to increase the speed of pg merging?
Our alternative is to create a new pool and transfer the data
Regards,
Justin
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