[DRBD-user] CPU Util for DRBD resources

Lars Ellenberg lars.ellenberg at linbit.com
Fri Nov 11 10:28:43 CET 2016

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

On Thu, Nov 10, 2016 at 03:15:40PM +0000, pillai bs wrote:
> On Tue, Nov 01, 2016 at 07:02:02AM +0000, pillai bs wrote:
> > > Hi Experts,
> > >
> > >
> > > Is there a possible way to monitor CPU Util for the drbd resource.
> > > Actually am getting cent percent utilization even i dont have much
> > > load.
> > >
> > > Am maintaining my setup with three blocks one for Data, other for
> > > configurations and the other for logs which was logically mounted.
> >
> > DRBD version?
> My DRBD Version is "8.3.11 "

You want to learn to quote.
It will make your life in the 'net much easier.

> %100 util does not mean it cannot take any more.  "I aggree"
> It only means that "most of the time" a new request is submitted before
> previous requests have been completed, or maybe "back to back" with the
> completion.
> Here "back to back" u meant it is synchronizing ??

No. I mean a new requet will be sumitted before previous requests have
been completed, or immediately after, leaving no time for the device to
be "idle". Nothing to do with resync.

I tried to explain what "utilization" is in this context.

> My question is
> why the "drbd2" alone utilizing CPU more than drbd1/drbd0
> SInce it is logicaly mounted, why not the actual "dm-9" shows very minimal util of CPU.

That "%util" column you see in iostat output is NOT cpu,
but *device* utilization, and just measures the fraction of time
the device has had "in-flight IO".

Also, it is very likely that this is simply wrong,
because the the "in-flight" counter looks wrong.

Let's do this the other way around:
 * do you have any problems with performance,
   or just with those statistics, which are likely simply wrong?
 * do statistics improve, if you upgrade your DRBD to a version that
   is less than five years old?

> Depending on usage patterns, and network and IO backend latencies,
> 100% util may even be expected.

: Lars Ellenberg
: LINBIT | Keeping the Digital World Running
: DRBD -- Heartbeat -- Corosync -- Pacemaker

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