Am 28.02.2018 um 16:09 schrieb Patrick Donnelly:
> On Tue, Feb 27, 2018 at 3:27 PM, Oliver Freyermuth
> <freyerm...@physik.uni-bonn.de> wrote:
>> As you can see:
>> - Name collision for admin socket, since the helper is already running.
> 
> You can change the admin socket path using the `admin socket` config
> variable. Use metavariables [1] to make the path unique.

Thanks for the link - did not know these yet :-). 

> 
>> - A second helper for the same mountpoint was fired up!
> 
> This is expected. If you want a single ceph-fuse mount then you need
> to persist the mount in the host namespace somewhere (using bind
> mounts) so you can reuse it. 

I still have to wonder how ntfs-3g does it - I don't see a persisted mount on 
the host,
i.e. nothing in /etc/mtab or with "mount" after the "umount" on the host. 
Still, when I try "mount" again on the host, the existing helper which is 
taking care of the child namespace
"adopts" the mount in the host namespace instead of spawning a new helper. 

My best guess (without any knowledge about Fuse...) would be that the new mount 
request shortly spawns a new helper,
which finds the old helper (via an admin socket, SHM or whatever - or maybe 
Fuse offers enumeration of other helpers?), 
and tells it to take care of the new mount, before it exits quickly. 

> However, mind what David Turner said
> regarding using a single ceph-fuse client for multiple containers.
> Right now parallel requests are not handled well in the client so it
> can be slow for multiple applications (or containers). Another option
> is to use a kernel mount which would be more performant and also allow
> parallel requests.

The kernel mount is sadly out - we need quota support :-(. 

Since we are currently network bandwidth limited (in huge file case) and MDS 
limited (in metadata ops / small file case), 
I expect the gains would be small (and come with a cost of a factor 28 of 
memory for ceph-fuse on the client machines,
and likely even higher MDS load since there are more clients). 
If I find some way to do this unprivileged, I'll give it a try, so many thanks 
for all the info! 

Cheers,
        Oliver

> 
>> - On a side-note, once I exit the container (and hence close the mount 
>> namespace), the "old" helper is finally freed.
> 
> Once the last mount point is unmounted, FUSE will destroy the userspace 
> helper.
> 
> [1] 
> http://docs.ceph.com/docs/master/rados/configuration/ceph-conf/?highlight=configuration#metavariables
> 

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