> Yes, single threaded, because the contention to the various files and the cost of serialisation would likely negate the benefits of using multiple threads.

Multithreaded does not mean multiple files.

> But not using DirectI/O so writes end up in memory and only get flushed if it hits the commit count, or periodically - so, particularly for local disks, HDDs or SSDs, this in practice never blocks for more than a few ms when flushing, if at all.

Unless you are actually using it under a high throughput scenario which is why you would use a lib like this. It will work great until you hit the actual flush point, then possibly block for seconds even minutes.

If your performance needs are high, mandating XFS is not unreasonable.