Cray System Management Documentation > Cray System Management (CSM) Administration Guide > utility storage > Shrink Ceph OSDs

Shrink Ceph OSDs

This procedure describes how to remove an OSD(s) from a Ceph cluster. Once the OSD is removed, the cluster is also rebalanced to account for the changes. Use this procedure to reduce the size of a cluster or to replace hardware.

Prerequisites

This procedure requires administrative privileges.

Procedure

Log in as root on the first master node (ncn-m001).
Monitor the progress of the OSDs that have been added.
```
ceph -s
```
View the status of each OSD and see where they reside.
```
ceph osd tree
```
Reweigh the OSD(s) being removed to rebalance the cluster.

The first two substeps below can be skipped if there is a down drive and OSD.
1. Change the weight of the OSD being removed to 0.
  
  The OSD_ID value should be replaced with the ID of the OSD being removed. For example, if the ID is osd.1, the OSD_ID value would be 1 in the command below.
```
ceph osd reweight osd.OSD_ID 0
```
2. Change the weight in the CRUSH map to 0.
```
ceph osd crush reweight osd.OSD_ID 0
```
3. Prevent the removed OSD from getting marked up.
```
ceph osd set noup
```
Remove the OSD after the reweighing work is complete.
1. Take down the OSD being removed.
```
ceph osd down osd.OSD_ID
```
2. Destroy the OSD.
```
ceph osd destroy osd.OSD_ID
```
3. Remove the OSD authentication key.
```
ceph auth rm osd.OSD_ID
```
4. Remove the OSD.
```
ceph osd rm osd.OSD_ID
```
5. Remove the OSD from the CRUSH map.
```
ceph osd crush rm osd.OSD_ID
```
6. Remove references to the OSDs on the storage node(s) they were located on.
  
  The following commands must be run on the storage node(s) that held the OSDs being removed.
```
umount /var/lib/ceph/osd/ceph-OSD_ID
rm -rf /var/lib/ceph/osd/ceph-OSD_ID
```
Clear the flags that were set earlier in the procedure.
```
ceph osd unset noup
```
Monitor the cluster until the rebalancing is complete.
```
ceph -s
```