Re: xl stack problems on CentOS6 XEN4

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Hi George,

I already outlined the drbd-stuff on xen-users (see attachement). Yes - elrepo is right on mark.

Excerpt:
"The script (/etc/xen/scripts/block-drbd) I am using is from drbd84-utils-8.9.2-1.el6.elrepo.x86_64 - and already seems to contain the "drbd or phy" case;
both in the add and the remove branch.

CentOS6 XEN4 is based on the Kernel 3.10.68-11.el6.centos.alt.x86_64 which has drbd 8.4.3 built in."

Excurse: As for SLES 11 there are two possibilities:
a) official: Buy the HAE license (quite expensive). There is a drbd-stack built into it (based on drbd 8.4)
b) inofficial: Compile your own drbd-srpm. That will contain the needed block-drbd as well, as part of the drbd-xen rpm. 

Back to my problem:

Your patch does not fit my sources:
http://vault.centos.org/6.6/xen4/Source/SPackages/
I am currently on XEN 4.4.2-2 - your patch is for 4.5?

Can you please backport your patch to 4.4.2-2?


Kind regards

Nils



-----Ursprüngliche Nachricht-----
Von: George Dunlap [mailto:george.dunlap@xxxxxxxxxxxxx] 
Gesendet: Montag, 18. Mai 2015 18:47
An: Hildebrand, Nils (BIT II 9); centos-virt@xxxxxxxxxx
Betreff: Re: xl stack problems on CentOS6 XEN4

[Switching to CentOS-virt, as I think that's probably actually a more
appropriate venue]

On 05/11/2015 02:52 PM, Hildebrand, Nils (BIT II 9) wrote:
> I am currently in the process of replacing my SLES11 SP3 Dom0s with CentOS6 XEN4 (at the moment: proof of concept with a test-cluster).
> 
> I want to use the new xl-stack, instead of the old xm-stack, too.
> 
> So far I stumbled across a number of minor glitches which could be worked around, I got DomUs with CentOS6 and CentOS 5 PV up and running with drbd-disk-backend (primary/secondary mode).
> 
> But now I am stuck at the problem that pygrub does not seem to know about drbd-devices.

I've never used drbd myself, but poking around a little bit, it seems
that the SLES has drbd pacakages, one of which includes block scripts
for Xen (drbd-xen).

Looking at CentOS 6, I don't immediately see any drbd packages.  Are you
using the packages from elrepo, perhaps?

In particular, do you have the Xen block scripts in
/etc/xen/scripts/block-drbd?

 -George
--- Begin Message --- 
Hi Ian,

following the link you provided:
http://lists.xen.org/archives/html/xen-devel/2014-02/msg01190.html

Looks indeed similar to my output
BUT: The following lines are missing on my output:

>> libxl: debug: libxl.c:2605:libxl__device_disk_local_initiate_attach:
>> trying to locally attach PHY device drbd-remus-test with script
>> block-drbd

I can not even see an attempt to call "block-drbd" in my debug-output.

Yes, vmname=xlnur079.

Making drbd primary does not create a device in /dev/ though - hence my workaround: cd "/dev/drbd/by-res/" before xl create. That's the place where xlnur079 (or at least an symbolic link with that name) resides.

The script (/etc/xen/scripts/block-drbd) I am using is from drbd84-utils-8.9.2-1.el6.elrepo.x86_64 - and already seems to contain the "drbd or phy" case;
both in the add and the remove branch.

CentOS6 XEN4 is based on the Kernel 3.10.68-11.el6.centos.alt.x86_64 which has drbd 8.4.3 built in.
In your mentioned link drbd 9.0 is being handled.

BTW: "remove" seems to be working without problems: xl shutdown will switch the drbd-device from primary to secondary (which in my case is bad, since the switch on create back onto primary is missing, which makes the reboot of the DomU fail).

The question now is (I think): Why is block-drbd not being called on create although the xl-parser knows about block-drbd?

So momentarily this looks indeed like a libxl problem.

Time to contact xen-devel, or can we do some deeper digging beforehand?


With kind regards

Nils








-----Ursprüngliche Nachricht-----
Von: Ian Campbell [mailto:ian.campbell@xxxxxxxxxx]
Gesendet: Dienstag, 12. Mai 2015 14:55
[...]
> xl create -n shows in the disk-section:  "script": "block-drbd"

That's good/expected.

> So yes - it seems that during (real?) creation the xl-parser does not
> seem to get the right disk-device-type and assumes "phy" instead of
> "drbd".

phy is correct, I think. the drdb: prefix translates into the use of the
block-drdb script which is supposed to make the device available to
dom0.

Xen doesn't provide block-drdb, I think it comes from the drdb project
itself. It's possible that something in libxl is incompatible with that
3rd party script, although I'm sure I've heard rumours of it working
(perhaps not with pygrub?).

http://lists.xen.org/archives/html/xen-devel/2014-02/msg01190.html might
be relevant here.


I take it that "xlnur079" is the "vmname" from:
        disk = [ ‘drbd:vmname,xvda,w’ ]
?

It seems that pygrub is being invoked onto xlnur079 directly, whereas I
would have expected the drdb script to have mapped that into some device
or other under /dev/. Perhaps updating the script will make that work
properly?

TBH, I'm struggling to find the code which invokes the script in this
pygrub case. If updating your block-drdb (per that link) doesn't help
then it seems possible you've found a deficiency in the libxl
arrangements here :-( If that turns out to be the case please could you
post that as a bug report to the xen-devel list.
http://wiki.xen.org/wiki/Reporting_Bugs_against_Xen

Thanks,
Ian.

--- End Message ---
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