On 20/1/21 9:54 pm, Michal Rostecki wrote:
On Wed, Jan 20, 2021 at 08:30:56PM +0800, Anand Jain wrote:
I ran fio tests again, now with dstat in an another window. I don't
notice any such stalls, the read numbers went continuous until fio
finished. Could you please check with the below fio command, also
could you please share your fio command options.
That's the fio config I used:
https://gitlab.com/vadorovsky/playground/-/blob/master/fio/btrfs-raid1-seqread.fio
The main differences seem to be:
- the number of jobs (I used the number of CPU threads)
- direct vs buffered I/O
fio \
--filename=/btrfs/largefile \
--directory=/btrfs \
--filesize=50G \
--size=50G \
--bs=64k \
--ioengine=libaio \
--rw=read \
--direct=1 \
--numjobs=1 \
--group_reporting \
--thread \
--name iops-test-job
It is system specific?
With this command, dstat output looks good:
https://paste.opensuse.org/view/simple/93159623
So I think it might be specific to whether we test direct of buffered
I/O. Or to the number of jobs (single vs multiple jobs). Since the most
of I/O on production environments is usually buffered, I think we should
test with direct=0 too.
It explains the stall for now, so it might be reading from the cache
so there was actually no IO to the device.
Agreed it must be tested with the most common type of IO. But as the
cache comes into play I was a bit reluctant.
Thanks, Anand
Cheers,
Michal
