Can you elaborate on what's so wrong with EBS? Are you thinking more about performance, or reliability?

I'm wondering in particular what you'd suggest in cases where RDS is not an option, if you're running your own MongoDB server or something like that. I don't think S3 is really an option there, is it?

Or would you tend to do everything on the instance store and periodically do a manual snapshot to S3?

It is not mentioned in the docs, but not only EBS performance is unreliable, but it is also not uncommon to get a "stuck" EBS volume, where no I/O operations go through at all. So you have to a) monitor and be ready to take action on "dead" hosts stuck on IO and b) not completely rely on EBS as perfect (it is possible to recover data, in most cases, but it is much easier if you can just create a new one and kill the misbehaving volume, automatically).

So in case of running custom data-intensive setup you could: 1. create a RAID out of several EBS volumes, maintain that - predictable speed, much better reliability 2. easier if you need a small scale solution - regular ebs snapshots and be ready to lose some inbetween snapshot data. Also, I think performance of disk is not a big issue in MongoDB case, so case 2 might be enough for your application. EBS failures are rare, afterall, so unless your data is critical and there is no way to do replication, snapshots would do.

EBS performance is notoriously variable by orders of magnitude. Amazon is working on this, however my personal belief is that using block storage creates an undesirable link between your storage and compute layers. Using S3, RDS or another NoSQL solution is a far more modular approach.

That being said, all apps are different and some may need block storage. I'm not saying it should not be used, however when making that decision the relation and hard dependencies created should be understood.

Er, RDS is (a) SQL (b) backed by EBS.

Understood, however AWS manages the association to block level storage, as well as the performance tuning. You can still operate with ephemeral compute decoupled from storage.

EBS volumes are analogous to hard drives. They're reliable... until they fail. So keep backups. This is easily done with EBS snapshots, (which are persisted to S3).