[DRBD-user] Still experiencing resource spikes

Prater, James K. jprater at draper.com
Tue Dec 18 15:29:35 CET 2012

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

Hello Lionel,

  The kernel version is 2.6.32-279.2.1.el6.x86_64 (RHEL does not yet incorporate DRBD in the kernel natively).  They (REDHAT), back port
version 3.x.x kernel features into 2.6.xx code tree.   So DRBD 8.4.2 is added as a loadable module.   This problem that we are experiencing  did not show up during testing.   It only reared its ugly head after being rolled into production.   I will take a look using 
"watch grep dirty /proc/vmstat".



-----Original Message-----
From: drbd-user-bounces at lists.linbit.com [mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of Lionel Sausin
Sent: Tuesday, December 18, 2012 5:55 AM
Cc: drbd-user at lists.linbit.com
Subject: Re: [DRBD-user] Still experiencing resource spikes

Le 18/12/2012 10:30, Andreas Kurz a écrit :
> That's quite a lot ... you also tuned vm.dirty_background_bytes and 
> vm.dirty_bytes to a reasonable low value? .... to avoid regular heavy 
> data write-out.... Regards, Andreas
I'd look into this too, although with the given config and the default 10% threshold for background writes of dirty pages, it should kick in for ~12 Gbytes of dirty. Let's say 120 Gbits get sent over the 20Gb/s link, that clean all up in a few seconds shouldn't it ?

I hope I'm not just adding noise, but if the kernel is old enough, there are cases where the write load is high enough for a sync operation to never end. Maybe that affects you?
In any case, it's worth running a "watch grep dirty /proc/vmstat" while the i/o block : if the cleaner is kicking in, nr_dirty should decrease down to almost zero. If it goes down an up again and again, maybe the write load is too high for a sync() to finish.

Lionel Sausin
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