Maildirs on AWS EFS

[Bert JW Regeer]

> On Mar 20, 2019, at 23:33, Rodolfo Gonzalez via dovecot <dovecot at dovecot.org> wrote:
> 
> Hello,
> 
> AWS released one month ago a EFS system with administered life cycle, which means that files not accessed in the last 30 days are moved to a lower cost storage tier. Currently I hold my e-mail, delivered to Maildir++ folders by postfix and retrieved with Dovecot, in standard EBS volumes. This has the disadvantage that I need to allocate more than enough space to ensure that the volume won't get filled too soon. And this costs. Changing to standard EFS wasn't an option, since it's way more expensive than EBS. But, with the new system, costs are lower.
> 
> I just have a doubt in the technical side: is it safe to have the email in EFS? I've read experiences about storing in S3 and using a driver to mount the bucket, and it seems that it's not a very good option. But EFS works like NFS4. Does anyone have experience mounting an EFS to store maildirs?
> 
> Thanks in advanced,
> Rodolfo.

I would not recommend storing your files on EFS. EFS has an average 5ms access latency per file (it can spike higher, at $WORK we have seen as high as 20msec). So if you have a 1000 files and need to call stat on them, you are at least 5000 msec later. On top of that you get a max of 7000 IOPS, so if a user moves a lot of messages around you start getting even more latency and issues.

Also, unless you keep terabytes worth of data, you are going to get really slow transfer/throughput because only once you hit certain terabyte thresholds do they increase the throughput.

You also have to massively parallelize your access for it to be worth it (and then you hit the 7000 IOPS limit). You'll be really disappointed with the performance of EFS.