btw, I think you meant that *slower* devices may need a larger queue to
saturate,
because if the device is fast, 256MB inflight is probably enough... So
you are solving
for the "consumer grade contemporary disks".
No, faster devices. The context here is random writes. The more of
those that are in the queue on the server, the more chance it has to
re-order or coalesce requests.
Umm, what would reorder help with if writes are random?
We don't want the device to go idle so we want lots of data buffered.
It will take the client some moments to respond to the client-side queue
dropping below a threshold by finding some pages to write and to submit
them. We don't want those moments to be long enough for the server-side
queue to empty.
Yes I agree. I was just arguing that the faster the device is, the lower
the completion
latency is. Meaning, if a device has a write-latency of 1us, you need a
shorter queue than
a device that has a write-latency of 100ms.
Anyways, we're getting side-tracked...
