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

[Alex Crow]

On 03/07/16 13:06, Volker Lendecke wrote:
> On Fri, Jul 01, 2016 at 10:00:21AM +0100, Alex Crow wrote:
>> We've had a strange issue after following the recommendations at
>> https://wiki.samba.org/index.php/Ping_pong, particularly the part
>> about mmap coherence. We are running CTDB/Samba over a MooseFS
>> clustered FS, and we'd not done the ping-pong before. After finding
>> that the mmap coherence test did not pass, we changed "use mmap" to
>> "no" in smb.conf.
> "use mmap" only affects tdbs, which should not sit on the clustered
> fs, they should *always* be on a local file system like ext4, assuming
> you're using Linux. The wiki page above states that it's not
> absolutely essential to provide mmap coherence, so you should not
> bother too much.
>
> Or are you putting tdb files on moosefs?
>
> BTW, the straces you're seeing are probably not real spins, that's
> traverses. With 10000 hash chains, that will be 10000 preads. That's
> just taking time. If the tdbs sit on moosefs, it might actually be
> true that it does not like that. But as I said: Never put tdbs on a
> cluster file system. If cluster file systems did that access pattern
> fine, ctdb would not exist :-)
>
> Volker

Hi Volker,

I've only put the "private dir" onto MooseFS, as instructed in the CTDB
docs.

So, in that case, I'm assuming from your comments that it is no worry
that the mmap test does not pass on the MooseFS mounts?

The "private dir" contains these files:

-rw-------+ 1 root root   24576 Jun 23 19:48 netlogon_creds_cli.tdb
-rw-------+ 1 root root  421888 Jun 23 19:48 passdb.tdb
-rw-------+ 1 root root  430080 Jun 23 19:47 secrets.tdb
drwxr-xr-x+ 3 root root 1001200 Jun 23 19:48 smbd.tmp

It just strikes me as odd that "use mmap = no" causes such a slowdown in
the the case I only have these files on my clustered FS. The timestamp
of all those files is the last time I joined one of the member servers
to the domain.

More worrying is that the rw ping-pong (no mmap) does not work properly
even when I mount my MooseFS with -o mfscachemode=none, which is not
supposed to do any local page/file cache and yet still I get
inconsistent results when adding and removing ping_pong tests on other
nodes (ie increment count does not always match running test nodes). I
have raised this with the MooseFS chaps and am waiting for a response.

Many thanks

Alex



--
This message is intended only for the addressee and may contain
confidential information. Unless you are that person, you may not
disclose its contents or use it in any way and are requested to delete
the message along with any attachments and notify us immediately.
This email is not intended to, nor should it be taken to, constitute advice.
The information provided is correct to our knowledge & belief and must not
be used as a substitute for obtaining tax, regulatory, investment, legal or
any other appropriate advice.

"Transact" is operated by Integrated Financial Arrangements Ltd.
29 Clement's Lane, London EC4N 7AE. Tel: (020) 7608 4900 Fax: (020) 7608 5300.
(Registered office: as above; Registered in England and Wales under
number: 3727592). Authorised and regulated by the Financial Conduct
Authority (entered on the Financial Services Register; no. 190856).