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Rephrase the power of 2 part

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Joshua Boniface 2020-11-14 11:58:03 -05:00
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@ -95,7 +95,7 @@ This guide will walk you through setting up a simple 3-node PVC cluster from scr
For example, to create a pool named `vms` with 256 placement groups (a good default with 6 OSD disks), run the command as follows: For example, to create a pool named `vms` with 256 placement groups (a good default with 6 OSD disks), run the command as follows:
`$ pvc storage pool add vms 256` `$ pvc storage pool add vms 256`
**NOTE:** Ceph placement groups are a complex topic; as a general rule it's easier to grow than shrink, so start small and grow as your cluster grows. The general formula is to calculate the ideal number of PGs is `pgs * maxcopies / osds = ~250`, then round `pgs` up to the next power of 2; generally, you want as close to 250 PGs per OSD as possible, but no more than 250. With 3-6 OSDs, 256 is a good number, and with 9+ OSDs, 512 is a good number. Ceph will error if the total number exceeds the limit. For more details see the Ceph documentation and the [placement group calculator](https://ceph.com/pgcalc/). **NOTE:** Ceph placement groups are a complex topic; as a general rule it's easier to grow than shrink, so start small and grow as your cluster grows. The general formula is to calculate the ideal number of PGs is `pgs * maxcopies / osds = ~250`, then round `pgs` down to the closest power of 2; generally, you want as close to 250 PGs per OSD as possible, but no more than 250. With 3-6 OSDs, 256 is a good number, and with 9+ OSDs, 512 is a good number. Ceph will error if the total number exceeds the limit. For more details see the Ceph documentation and the [placement group calculator](https://ceph.com/pgcalc/).
**NOTE:** As detailed in the [cluster architecture documentation](/cluster-architecture), you can also set a custom replica configuration for each pool if the default of 3 replica copies with 2 minimum copies is not acceptable. See `pvc storage pool add -h` or that document for full details. **NOTE:** As detailed in the [cluster architecture documentation](/cluster-architecture), you can also set a custom replica configuration for each pool if the default of 3 replica copies with 2 minimum copies is not acceptable. See `pvc storage pool add -h` or that document for full details.