Just create this bug to track it status and not miss it, because it was early mentioned in separate email.

From email message

[root@qian tests]# ../utils/lctl pcc add /mnt/lustre /mnt/pcc -p "projid={100} roid=2"

lctl pcc pcc: error: setting llite.lustre-ffff9952eece7000.pcc='add /mnt/pcc projid={100} roid=2': Invalid argument (22)

Details:

According to the Lustre manual user can add PCC cache with rwid and roid options.

Attempt to add cache with roid option only was failed. So as workaround it is necessary to use rwid option.