Bug#827322: multipath-tools: Not all paths discovered when large number of paths are present

[Andrew Patterson]

On Mon, 20 Jun 2016 16:40:29 -0600 Andrew Patterson <andrew.patterson at hpe.com> wrote:
> On Thu, 16 Jun 2016 15:19:22 +0530 Ritesh Raj Sarraf <rrs at debian.org> wrote:
> > Control: tag -1 +pending
> > 
> > On Wed, 2016-06-15 at 13:03 -0600, Andrew Patterson wrote:
> > > For most users this is not an issue. How many systems are going to use
> > > that many LUNs?
> > > 
> > 
> > I agree.
> > 
> > > One counter-example is using one or more FC LUNs per VM guest on a
> > > host. In such a case, one can just modify /etc/sysctl.conf to increase
> > > the setting. 
> > 
> > Yes. Most hypervisors may want this. But again, like you said, most users do not
> > map that many LUNs. And recommended practice is to have a VM backed by a file
> > backend mostly.
> 
> 
> OpenStack/cinder can (and is) be uses to provision VMs with networked
> drives. It is pretty common for cloud applications.  I don't know what
> a practical limit for the number of volume per VMs per host should be.
> 
> 
> > 
> > > We can run into problems when using
> > > multipath-tools-boot. In this case, we use the default kernel settings
> > > for aio-max-nr since multipath is run from the initramfs. I have
> > > worked around this by modifying the script in
> > > /usr/share/initramfs/scripts/local-top/multipath to temporarilly set
> > > aio-max-nr to 1048576 while doing discovery.
> > 
> > 
> > So, I'll just add this to README.Debian. There's not much that we can do beyond
> > documenting such behavior.
> 
> I will work on patch to have a user-configurable setting of aio-max-nr
> in the initramfs. You can then decide if it is worth it to apply it.
> 
> In the meantime, the README.Debian change sounds fine to me.
> 

Here is a patch that copies the fs.aio-max-nr setting to the
initramfs. There is more to do to solve the problem with booting with
many LUNs, but this is a prerequisite for completely solving that
issue.  This patch assumes that the patch in:

https://bugs.debian.org/cgi-bin/bugreport.cgi?att=1;bug=827407;filename=multipath-tools-827407.patch;msg=30

has been applied. I can rework it if that one is not accepted.

Andrew

-- 
Andrew Patterson
Hewlett-Packard Enterprise
-------------- next part --------------
A non-text attachment was scrubbed...
Name: multipath-tools-827322.patch
Type: text/x-patch
Size: 2775 bytes
Desc: not available
URL: <http://lists.alioth.debian.org/pipermail/pkg-lvm-maintainers/attachments/20160623/778edb51/attachment.bin>