Re: Is there a faster way to merge PGs?

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Hit "send" too soon...

I meant to add that apparently, there's no way to increase pg merge. Moving data to a different pool is most likely much faster if you have the capacity (which you seem to have if you want to get rid of 1700 OSDs ;-) ).


Zitat von Eugen Block <eblock@xxxxxx>:

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@xxxxxxxxxxxxxx>:

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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