multi-directory, storage hierarchy, ephemeral awareness

[steveyen]

This is probably too big for one ticket/issue, but...

Many systems have multiple I/O devices. And, today's moss only writes to a single directory, so isn't able to leverage multi-device I/O concurrency/bandwidth.

Some of those devices will be faster than others (SSD vs HDD).

And, some might be ephemeral (ex: EC2 ephemeral storage) versus long-lived (ex: EBS).

It might be debatable whether a "sufficiently advanced moss of the future" should be aware of such things, or whether such concerns should instead remain (like today) as just the application's responsibility to shard their moss usage on their own and handle the movement of data amongst storage hierarchies on their own.