Does mongo *really* need a dedicated volume, if I need to back it up?
Yes, hot snapshot is easy and fast way to do backup... But of course there is also mongodump. Here is my crontab entry. Every hour, overriding current date backup.
SHELL=/bin/bash
DATEVAR=date +%d
    
31 * * * * /usr/bin/mongodump --host localhost -o /dbdata/dump$($DATEVAR) --gzip --oplog &gt;&gt; /dev/null 2&gt;&amp;1