Direct I/O performance – sequential 2MB operations
While important, random 4K performances are not the only factors to consider: for some application, high sequential speed is also vital. Let see how the schedulers react to bigger sized transfers.
First, 2MB sequential reads:
While the contenders are more or less tied here, the CFQ and deadline schedulers pull slightly ahead.
Now, 2MB sequential writes:
We see some differences here, with deadline showing the better score.
Let simulate a more complex scenario now, with concurrent read and write operations:
Again deadline pulls slightly ahead.
I left the heavier bench for the last IOMeter graph: a 4KB – 2MB read/write, random/sequential mixed workload:
Somewhat surprisingly, all schedulers are more or less in line here.
All in all, IOMeter shows that, when dealing with direct I/O, the I/O scheduler play a very important role. From the benchmark above, it seems that the best scheduler for direct I/O is deadline.