mdbox vs. maildir format

hey,

i am considering changing my mailbox format from maildir to mdbox. the reason for this is mainly, b/c i have (a) multiple large mailboxes with tens of thousands of mail files, and (b) most of these mails files have a size significantly smaller than the sector size of the disk.

so, since the emails themselves are only about nGB large, the disk space used is at least twice as much, if not even three times.

i know, hard disk space is 'cheap', but still...

but then i read at

https://doc.dovecot.org/admin_manual/mailbox_formats/dbox/

the following:

[...] you must not lose the dbox index files, as they can’t be
regenerated without data loss.

so, raid is mandatory, which is already the case, but what about backup? how can i achieve a backup/snapshot of both, the mdbox (nfs share) and the index files (local raid) and assure they are consistent?

greetings...