[Samba] Winbind process stuck at 100% after changing use_mmap to no

[Alex Crow]

On 14/07/16 14:51, Volker Lendecke wrote:
> On Thu, Jul 14, 2016 at 02:39:48PM +0100, Alex Crow wrote:
>>> The main hint I would like to give to the MooseFS developers is to get
>>> ping_pong -rw working. If you need any assistance in setting that up
>>> and getting arguments on why this is important, let us know!
>>>
>>> With best regards,
>>>
>>> Volker
>> Any arguments that I can pass on would be much appreciated.
> The main argument is that Windows applications tend to coordinate access
> to files via byte-range locks. They expect data coherency under those
> byte range locks, meaning that if a value is written under a brlock,
> the brlock is released, and another process reads the value under the
> brlock, the value written must be visible. If this is not guaranteed,
> then data corruption will likely happen. The main question to the
> MooseFS developers would be under which circumstances a value written
> via pwrite on node A is visible via pread on node B. ping_pong checks
> this sequentiality with fcntl byte range locks, which are the Posix
> way of serializing access to ranges of a file. If MooseFS gives other
> guarantees, we would like to know about them.
>
>> I've also had a try with RozoFS, which did not work as expected as
>> it only supports block-level locks (4096 bytes) so the first lock
>> prevent further locks in that block range, which naturally causes
>> ping_pong to stall. However I am told by their devs that this should
>> not be an issue for CTDB's recovery lock or Samba as they should not
>> need to lock ranges of less than a 4k, and they in fact integrate
>> CTDB for their customers.
> That's right. For the recovery lock this does not matter. But for plain
> file access it will. On RozoFS you should set "posix locking = no",
> but then you depend on external serialization via ctdb: With "strict
> locking = yes" (which is default), Samba does check byte range locks and
> this way serializes access to user files on RozoFS. This serialization
> however is not coordinated with the cluster file system in question,
> so the RozoFS developers might have to tell us about their approach to
> data coherency too.

So perhaps posix locking=no might be worth trying on MooseFS too?

I will pass on your comments in my support ticket with the MooseFS staff...

Thanks again and best regards

Alex

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