More on the zfs laptop journey
By user12625760 on Nov 25, 2005
Life on the laptop contiues with zfs. I'm more than happy.
I have one thing that i did change, that is I have switched the disk driver to use a fifo sort rather then a block address sort. This gives a slightly more predictable performance for each IO with the down side that it increases the overall throughput particularly of sequential writes.
This is done by adding queue="qfifo" to the lines in /kernel/drv/cmdk.conf
name="cmdk" class="dada" target=0 lun=0 class_prop="dada" queue="qfifo";
The potential issue here is that ZFS can dump lots of sequential writes onto the device and since the drivers queue depth is just 2 the rest end up on the wait queue ordered in increasing LBA. So if while this is going on the system needs to do an IO to the root or swap partitions that IO has to wait for all the ZFS writes to complete before it will get to the front of the queue. On a laptop that may not be the ideal situation as, particularly if you are short on memory you may want to page a binary in to continue working.
My next task it to prove this since the laptop feels faster when there is background IO with the qfifo setting in place but that is just a gut feeling.