Upcoming changes to Lustre for Sequoia (Lustre 2.3/2.4) require that the OST index always be specified when formatting OSTs. To prepare users for these changes, update the examples in the manual to always use the --index option with mkfs.lustre when formatting OSTs, and list it as a recommended option in the mkfs.lustre options. This is already accepted as standard practice for Lustre users today.