mdbox vs. maildir format

[Michael]

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...