[DRBD-user] Kernel hung on DRBD / MD RAID

Micha Kersloot micha at kovoks.nl
Tue Mar 6 10:05:10 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.


----- Oorspronkelijk bericht -----
> Van: "Andreas Bauer" <ab at voltage.de>
> Aan: drbd-user at lists.linbit.com
> Verzonden: Dinsdag 6 maart 2012 00:27:33
> Onderwerp: Re: [DRBD-user] Kernel hung on DRBD / MD RAID
> From:	Florian Haas <florian at hastexo.com>
> Sent:	Mon 05-03-2012 23:59
> > On Mon, Mar 5, 2012 at 11:45 PM, Andreas Bauer <ab at voltage.de>
> > wrote:


> > If you're telling your system to use an sync/verify rate that you
> > _know_ to be higher than what the disk can handle, then kicking off
> > a
> > verify (drbdadm verify) or full sync (drbdadm invalidate-remote)
> > will
> > badly beat up your I/O stack.
> > 
> > The documentation tells you to use a sync rate that doesn't exceed
> > about one third of your available bandwidth. You can also use
> > variable-rate synchronization which should take care of properly
> > throttling the syncer rate for you. But by deliberately setting a
> > sync
> > rate that exceeds disk bandwidth, you're begging for trouble. Why
> > would you want to do this?
> Because I want to badly beat up my I/O stack? The point of this
> exercise is to reproduce the kernel crash. So to stay with the
> image, the stack should be able to take a beating without dying in
> the process.

In reality it happens often when a MD resync is running (even when throttled to f.e. 1000 K/s)
and DRBD is also resyncing. When you then look at /dev/mdstat you'll find the sync rate is slowing down to zero.

We do use DRBD on top of raid1 on several other servers without problems. We do use Xen on top of raid1 on several other servers without problems.


Micha Kersloot

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