[DRBD-user] drbd turned on me, and bit my hand this morn

Brad Barnett lists at l8r.net
Sat Dec 10 15:52:24 CET 2005

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

On Sat, 10 Dec 2005 14:57:01 +0100
Lars Ellenberg <Lars.Ellenberg at linbit.com> wrote:

> / 2005-12-10 07:39:34 -0500
> \ Brad Barnett:
> > 
> > 
> > 
> > 
> > Ok, my drbd rebuild is complete, and I can do some testing this
> > weekend at specific planned times.
> > 
> > Before I do, I'd like to ask a few questions.  I might as well try to
> > tune drbd as best as I can, beforehand. ;)
> > 
> > Anyhow, as far as I can tell, the syncer seems to be for the sync
> > process ... and not normal data transfer between the two drbd nodes? 
> > I ask, because I actually had to turn off my full sync process during
> > the day, as nfs access dropped to approximately 1/50th the speed with
> > it on.
> > 
> > Is the sync process supposed to "give way" to the normal data updates
> > between the nodes?  Or, during a full sync, does drbd store local
> > changes on the primary.. and just ignore sending anything to the
> > secondary?
> Syncer access and application writes are concurrent.
> They are not prioritized. This is on the wishlist, though.
> You "give way" by setting the sync rate to something lower than your
> actual bandwith, thereby "reserving" the rest of the bandwidth for your
> applications.

Ok, great... so I can set this relatively low, and sync over three days
instead of one... and have lots of bandwidth left.  Bonus.

> BTW, you won't see a Full Sync with drbd 0.7 and later, except for the
> initial one, or in case one of the lower level storages gets physically
> replaced, and you _request_ a full sync again by invalidating that
> device.

True.. but I'm going to be doing some testing on the problem I found
earlier, to see if I can duplicate it and find the source.  I'll probably
do a few full syncs when doing so, so I just want to get it running

> > If so, why was my access so slow during that full sync?  I tried
> > reducing my sync from 700000k to 250000k, but I saw no difference in
> Note that we are storage guys, not network guys.
> So think storage.
> This rate is given in Byte, not Bit.
> I seriously doubt your hardware can
> do sustained 250 Mega Byte transfer rate.

Ah.. ok.  Thanks.. I suppose you would have used b for bit, if that was
the case anyhow.. but unfortunately I see B and b used incorrectly so
often, I just assume bit now. :/  My mistake.

> > syncer rate/performance.  I have a crossover cable between two gigabit
> > network devices.. and dmesg as well as ethtool confirms this.
> > 
> > Any suggests for better usage while sync is happening.. or ways to
> > tune this baby?
> -- 
> : Lars Ellenberg                                  Tel +43-1-8178292-0  :
> : LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
> : Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
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