Imposing ZFS latency limits

[Dustin Wenz]

I'm trying to find a way to get lower read latency in ZFS when there is a failing disk in a mirror. The specific failure mode that I'm trying to handle is when a disk takes significantly longer than usual to respond to read requests, but is not so far gone that the OS drops it from the bus. In that case, the whole pool can become much less responsive than I think it needs to be.

Since ZFS has access to the data I'm reading through other members in a mirror, I would like ZFS to defer to the redundant disks when individual disk latency exceeds some threshold that I would define. Is there any provision for this in the FreeBSD ZFS implementation?

	- .Dustin