[Dovecot] mdbox: more then one altstorage

[Peer Heinlein]

The mdbox-format with the altstorage-feature is quite nice and important.

But we're having much more then >> 30 TB of maildata and doing an fsck
on huge partitions takes too much (down-) time for our mailsystem.

It would be much easier, if Dovecot would be able to use at least THREE
storage-paths for his m-Files (and not just TWO like now).

Having an altstorage1 and altstorage2, we would be able to move away all
mails from on altstorage-mountpoint, we could put this
storage-moungpoint into "maintenance" and do an fsck without Downtime
for Dovecot.


It would be nice having a doveadm-feature to put a altstorage-path in
"maintenance-mode", so to move easily away all m-files to other
alt-storage-paths and to let Dovecot know not to use this locked partition.


Having even more then 3 storage-paths would be nice for huge setups: In
this case we could easily use different SMALLER partitions without
having just two or three huge partitions > 15 TB.


The architecture of the altstorage-system is nice and simple. Wouldn't
it be easily possible to look (at least) in three, then just in two
places for a m-file?

What about a "hash_dir"-system for the storage? What about a
configuration-parameter like

altstorage_dirs=4

which would mean, that there are 4 storage-mountpoints that could be
addressed by "%m":

mail_location = mdbox:/vmail/%d/%n/mdbox:altstorage/alt/%m/%d/%n

In this case, Dovecot could easily use all existing partitions
automatically "round-robin".

Or maybe it would be better to tell Dovecot the partitions by:

altstorage_dirs_existing = 1,2,3,4
altstorage_dirs_newmail = 1,4

so it would be very easy to tell Dovecot in which partitions he has to
look for m-files and where he is allowed to save round-robin new
e-mails. With this setup it's easy to put a partition in maintenance mode.


Peer

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