Doubt about replacing alt storage disks

[Amol Kulkarni]

Hello,

I have a working setup of dovecot 2.2.19 on centos 6.
The mailbox format is mdbox. I've configured primary and alt storage.

Now I want to replace the disk of the alt storage only.

Broadly my plan to change it is as follows :
1. Mount the new disk on a temporary server.
2. Rsync data only from alt storage to the new disk - while the original
server is live. This may take a few days. In between altmove will happen on
the live disk.
3. Once the basic rsync is complete, stop all services on the live server
4. Mount the new disk on live server, in addition to live disk
5. Do final rsync - with the delete option
6. Unmount the live disk and mount new disk in its place
7. Start services

I've 2 doubts abt this plan :
1. I've tried the first part until step 2. After the first rsync, I found
unexpected differences between the m.* files on the live and new disk. The
new disk has some additional files for some users, which are not present on
the live disk. Since the rsync was run without delete option, these files
were not deleted from the new disk. Does altmove delete some m.* files to
reorganize mail ? Can end user mail deletion cause deletion of m.* files ?

2. I'm worried about commonly occuring problems with such movement :
duplicate mail download in pop / resync in imap / index corruption. Is
there any way to check integrity of data before switching to the new disk ?

Thanks in advance,
Amol.