[DRBD-user] the perfomance issuce with a physical volume synchronization

Lars Ellenberg lars.ellenberg at linbit.com
Fri May 20 11:11:32 CEST 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


On Fri, May 20, 2011 at 05:32:52PM +0900, Junko IKEDA wrote:
> Hi,
> 
> We are trying to configure a DRBD resource as a Physical Volume, using
> examples from the following document.
> http://www.drbd.org/users-guide/s-lvm-drbd-as-pv.html
> 
> DRBD works well, but there are some perfomance problems.
> We run "dd" like thie;
> # dd if=/dev/zero of=/mnt/dd/10GB.dat bs=1M count=10000 oflag=direct
> 
> then, "iostat" shows the strange output.
> # iostat -xmd 10 /dev/cciss/c0d3
> -------------------------------------------
>                    | wMB/s | w/s
> -------------------------------------------
> hdd              | 68.6     |  805
> drbd             | 47.3     |  910
> lvm on drbd   | 31.8     | 8140
> -------------------------------------------
> 
> In case of "lvm on drbd", w/s shows relatively large value compared to
> other cases,
> then CPU %util also increase to 100%,
> so DRBD sync/rsync performance drops significantly.
> Pacemaker detects it as DRBD's error.
> 
> Have anyone ever seen a similar problem?
> or is there some tips for physical volume settings?

DRBD version, LVM version, Device mapper version (kernel version),
distribution?

What about oflag=dsync instead of direct?
What about not specifying any oflag, but doing
# dd if=/dev/zero of=/mnt/dd/10GB.dat bs=1M count=10000 conv=notrunc,fsync

What about reads?
With iflag=direct?
Without without iflag, but still cache cold,
after an echo 3 > /proc/sys/vm/drop_caches?

Do you have an other data point with more recent (all of it),
especially with more recent LVM + upstream kernel?

Or on an older distributions?

> Hardware information;
> I/O scheduler: deadline
> partition size: 100GB
> CPU: 6 core x 2
> Memory: 12GiB
> HDD: SAS 10000rpm, 300GiB
> 
> Best Regards,
> Junko IKEDA
> 
> NTT DATA INTELLILINK CORPORATION

-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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