Re: backup postgresql with snapshot AWS

>
> IMHO the more you intertwine things you cannot be certain of because they operate outside of your particular VM's
spacewith a process that relies on them the more you are risking finding out that your assumptions are wrong the hard
way. You *shouldn't* get bit by this in a well-designed cloud or cluster system but that's not an acceptable word to
describethe expected results when it's important. 

One needs to understand their technology stack. You need to know where your data is after a sync() call… is it cached
inthe controller, some other application layer, or safely on disk? You also need to understand the relationship between
luns,volume managers, and filesystems and where your atomic operation are in your setup.    

i.e. If the filesystem spans multiple EBS volumes then you can’t use EBS snapshots otherwise you end up with a
corruptedfilesystem/database; however, if you use one filesystem per EBS volume then EBS snapshots work fine.  Amazon’s
ownRDS service uses EBS snapshots for backups.