Github issue 2258 openEBS repo is tracking this. At present this can be done by patch few resources. Pasting the content form the github workaround,

For expanding a cStor pool (type=striped) with additional disks.

A brief explanation cStor pool components Storage Pool CR (SP) - used for specifying the Disk CRs used by the pool. cStor Storage Pool CR (CSP) - used for specifying the unique disk path used by the pool. cStor Storage Pool Deployment and associated Pod. When the SPC spec is created with a set of disks, the cstor-operator will segregate the disks based on the node. And on each node, a cStor Pool will be created using the disks from that node. After the pool is provisioned, it can be expanded only by the disks already discovered on the same node.

The following steps are for expanding a single cStor Storage Pool and will need to be repeated on each of the cStor Pools corresponding to an SPC.

Step 1: Identify the cStor Pool (CSP) and Storage Pool (SP) associated with the SPC.

kubectl get sp -l openebs.io/storage-pool-claim=cstor-disk --show-labels

Storage Pools sample output:

NAME              AGE       LABELS
cstor-disk-i4xj   53m       kubernetes.io/hostname=gke-kmova-helm-default-pool-2c01cdf6-9mxq,openebs.io/cas-type=cstor,openebs.io/cstor-pool=cstor-disk-i4xj,openebs.io/storage-pool-claim=cstor-disk
cstor-disk-vt1u   53m       kubernetes.io/hostname=gke-kmova-helm-default-pool-2c01cdf6-dxbf,openebs.io/cas-type=cstor,openebs.io/cstor-pool=cstor-disk-vt1u,openebs.io/storage-pool-claim=cstor-disk
cstor-disk-ys0r   53m       kubernetes.io/hostname=gke-kmova-helm-default-pool-2c01cdf6-nh6w,openebs.io/cas-type=cstor,openebs.io/cstor-pool=cstor-disk-ys0r,openebs.io/storage-pool-claim=cstor-disk

From the above list, pick up the cStor Pool that needs to be expanded. The name of both CSP and SP will be same. The rest of the steps assume that cstor-disk-vt1u needs to be expanded. From the above output, also note down the node on which the Pool is running. In this case the node is gke-kmova-helm-default-pool-2c01cdf6-dxbf

Step 2: Identify the new disk that that need to be attached to the cStor Pool. The following command can be used to list the disks on a give node.

kubectl get disks -l kubernetes.io/hostname=gke-kmova-helm-default-pool-2c01cdf6-dxbf

Sample Disks Output.

NAME                                      AGE
disk-b407e5862d253e666636f2fe5a01355d     46m
disk-ffca7a8731976830057238c5dc25e94c     46m
sparse-ed5a5183d2dba23782d641df61a1d869   52m

The following command can be used to see the disks already used on the node - gke-kmova-helm-default-pool-2c01cdf6-dxbf

kubectl get sp -l kubernetes.io/hostname=gke-kmova-helm-default-pool-2c01cdf6-dxbf -o jsonpath="{range .items[*]}{@.spec.disks.diskList};{end}" | tr ";" "\n"

Sample Output:

[disk-b407e5862d253e666636f2fe5a01355d]
[sparse-ed5a5183d2dba23782d641df61a1d869]`

In this case, disk-ffca7a8731976830057238c5dc25e94c is unused.

Step 3: Patch CSP with the disk path details Get the disk path listed by unique path under devLinks.

kubectl get disk disk-ffca7a8731976830057238c5dc25e94c -o jsonpath="{range .spec.devlinks[0]}{@.links[0]};{end}" | tr ";" "\n"

Sample Output:

/dev/disk/by-id/scsi-0Google_PersistentDisk_kmova-n2-d1

Patch the above disk path into CSP

kubectl patch csp cstor-disk-vt1u --type json -p '[{ "op": "add", "path": "/spec/disks/diskList/-", "value": "/dev/disk/by-id/scsi-0Google_PersistentDisk_kmova-n2-d1" }]'

Verify that disk is patched by executing kubectl get csp cstor-disk-vt1u -o yaml and check that new disk is added under diskList.

Step 4: Patch SP with disk name The following command patches the SP (cstor-disk-vt1u) with disk (disk-ffca7a8731976830057238c5dc25e94c)

kubectl patch sp cstor-disk-vt1u --type json -p '[{ "op": "add", "path": "/spec/disks/diskList/-", "value": "disk-ffca7a8731976830057238c5dc25e94c" }]'

Verify that disk is patched by executing kubectl get sp cstor-disk-vt1u -o yaml and check that new disk is added under diskList.

Step 5: Expand the pool. The last step is to update the cstor pool pod (cstor-disk-vt1u) with disk path (/dev/disk/by-id/scsi-0Google_PersistentDisk_kmova-n2-d1)

Identify the cstor pool pod associated with CSP cstor-disk-vt1u.

kubectl get pods -n openebs | grep cstor-disk-vt1u

Sample Output:

cstor-disk-vt1u-65b659d574-8f6fp            2/2       Running   0          1h        10.44.1.8    gke-kmova-helm-default-pool-2c01cdf6-dxbf

Check the pool name:

kubectl exec -it -n openebs cstor-disk-vt1u-65b659d574-8f6fp -- zpool list

Sample Output:

NAME                                         SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
cstor-deaf87e6-ec78-11e8-893b-42010a80003a   496G   202K   496G         -     0%     0%  1.00x  ONLINE  -

Extract the pool name from above output. In this case - cstor-deaf87e6-ec78-11e8-893b-42010a80003a

Expand the pool with additional disk.

kubectl exec -it -n openebs cstor-disk-vt1u-65b659d574-8f6fp -- zpool add cstor-deaf87e6-ec78-11e8-893b-42010a80003a /dev/disk/by-id/scsi-0Google_PersistentDisk_kmova-n2-d1

You can execute the list command again to see the increase in capacity.

kubectl exec -it -n openebs cstor-disk-vt1u-65b659d574-8f6fp -- zpool list

Sample Output:

NAME                                         SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
cstor-deaf87e6-ec78-11e8-893b-42010a80003a   992G   124K   992G         -     0%     0%  1.00x  ONLINE