Re: [Nbd] question about i/o scheduling

[Peter Simons <simons@...813...>]

Hi Wouter,

 >> Now, it looks to me like my kernel performs too much write-buffering.
 >> When a large file is copied to an nbd-mounted partition, the initial 2
 >> MB or so are transferred at incredible speed; apparently, because the
 >> kernel just buffers the data. At one point, the kernel actually tries to
 >> transfer the data to the remote host, but that takes several minutes.
 >> During that time, the nbd-device is almost unusable for other processes
 >> because it accepts no more writes at all (and reads have a hard time
 >> getting through the network connection).
 >> 
 >> Has anyone else observed that phenomenon? Is there maybe a way to
 >> improve the situation?
 >
 > You can try to change the I/O scheduler. The default for most devices is
 > "cfq", but that isn't very useful for nbd. The 'deadline' one could
 > yield better results.

yes, that is what the README suggested. I am using the deadline
scheduler:

 $ cat /sys/block/nbd0/queue/scheduler 
 noop [deadline] cfq 

The problem occurs anyway.

Take care,
Peter