Runnin a chkdsk /r on an ISCSI drive
A ISCSI drive is not like a normal drive you can’t scheduled a chkdsk /r on startup as it’s not mounted on startup.
Dismount the iSCSI drive by going to Computer Management>Storage>Disk Management. Find the physical disk resource on which you want to run Chkdsk, take the entire drive offline.
This closes all of the handles to the physical disk. Then bring it online.
To do this, right-click the disk resource, and then click Bring on-line.
Now, you should be able to run chksdk /r.