Re: [Nbd] question about i/o scheduling
- To: firstname.lastname@example.org
- Subject: Re: [Nbd] question about i/o scheduling
- From: Peter Simons <simons@...813...>
- Date: Wed, 04 Aug 2010 11:21:31 +0200
- Message-id: <87zkx27mxw.fsf@...814...>
- References: <87k4o71sk2.fsf@...814...> <20100804032250.GF3885@...510...>
>> 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
$ cat /sys/block/nbd0/queue/scheduler
noop [deadline] cfq
The problem occurs anyway.