[cjbprime]

I've hit problems like reaching ENOSPC (even though the data extents were only 70% full) on a colocated server, and there isn't enough free space to run a balance operation to get more free space. (The docs literally suggest inserting a USB stick and adding it to your array to help make the balance work..)

Also, the fsck tool is still very immature. It takes many years to get good at detecting and recovering from corruption.

[yawniek]

had that same problem and additionally performance problems on ssds with fast writes (postgresql) even when turning off the COW