Very low disk performance on 5.x

[Petri Helenius]

Robert Watson wrote:

>
> The next thing that would be quite nice to measure is the rate of I/O 
> transactions per second we can get to the disk using the disk device 
> directly, with a minimal transaction size.  I have a vague 
> recollection that you have to be careful in Linux because their 
> character device nodes for disk devices are buffered, and you really 
> want unbuffered I/O.


I noticed that changing vfs.read_max from the default 8 to 16 has a 
dramatic effect on sequential read performance. Increasing it further 
did not have measurable effect.

Pete