ZFS vs EXT4 - ZFS wins
I have said this numerous times and now I am able to back my claims with results
When given multiple dedicated disks, ZFS is considerably faster than EXT4. The notable exceptions are
a) No Sync/Fsync tests. Meaningless in any case other than for academic purposes.
b) Very simple configurations, such as a single disk, single HW Raid volume, or a simple mirror.
The reason for this is that testing of software cannot be hardware blind. Limited hardware will always make simpler software look better. All the light-weight desktop environments are a point in case. On older systems with limited hardware resources, the heavy-weights will simply not have the leg room to come into their own right.
Similarly ZFS has got a lot of features which are realy good when you have the right hardware, but on limited hardware the limited performance may outweight the benefits, depending on your requirements.
Two points that I must raise:
Firstly: Testing ZFS on a solid state disk eliminates its ability to hide the latencies of physically rotating disk drives. Don't get me wrong: SSDs are not bad for ZFS, on the contrary traditional hard disk drives are bad for EXT2/3/4
Secondly: I watched CPU and run-queue while I performed the tests. With ZFS there was typically arround 80% CPU idle, with EXT4 it varied arround the 66% mark. This is on an otherwise idle system.
The importance of this is two-fold: Firstly the CPU was not the bottle neck in this case, running at 2Gbps. I will soon replace the disk subsystem with one that supports 8Gbps. The disks/busses will there be more able to keep up with the requests, which means that the CPU will have to work harder to keep the disks fed with requests. If everything scales as expected, EXT4 will run into a CPU bottleneck first.
Secondly even with the existing disk/FC configuration, if one adds a workload, there will be less CPU time available for the file system. ZFS will then suffer less.