On Tue, Apr 30, 2019 at 8:01 AM Oliver Freyermuth
<freyerm...@physik.uni-bonn.de> wrote:
>
> Dear Cephalopodians,
>
> we have a classic libvirtd / KVM based virtualization cluster using Ceph-RBD 
> (librbd) as backend and sharing the libvirtd configuration between the nodes 
> via CephFS
> (all on Mimic).
>
> To share the libvirtd configuration between the nodes, we have symlinked some 
> folders from /etc/libvirt to their counterparts on /cephfs,
> so all nodes see the same configuration.
> In general, this works very well (of course, there's a "gotcha": Libvirtd 
> needs reloading / restart for some changes to the XMLs, we have automated 
> that),
> but there is one issue caused by Yum's cleverness (that's on CentOS 7). 
> Whenever there's a libvirtd update, unattended upgrades fail, and we see:
>
>    Transaction check error:
>      installing package libvirt-daemon-driver-network-4.5.0-10.el7_6.7.x86_64 
> needs 2 inodes on the /cephfs filesystem
>      installing package 
> libvirt-daemon-config-nwfilter-4.5.0-10.el7_6.7.x86_64 needs 18 inodes on the 
> /cephfs filesystem
>
> So it seems yum follows the symlinks and checks the available inodes on 
> /cephfs. Sadly, that reveals:
>    [root@kvm001 libvirt]# LANG=C df -i /cephfs/
>    Filesystem     Inodes IUsed IFree IUse% Mounted on
>    ceph-fuse          68    68     0  100% /cephfs
>
> I think that's just because there is no real "limit" on the maximum inodes on 
> CephFS. However, returning 0 breaks some existing tools (notably, Yum).
>
> What do you think? Should CephFS return something different than 0 here to 
> not break existing tools?
> Or should the tools behave differently? But one might also argue that if the 
> total number of Inodes matches the used number of Inodes, the FS is indeed 
> "full".
> It's just unclear to me who to file a bug against ;-).
>
> Right now, I am just using:
> yum -y --setopt=diskspacecheck=0 update
> as a manual workaround, but this is naturally rather cumbersome.

This is fallout from [1]. See discussion on setting f_free to 0 here
[2]. In summary, userland tools are trying to be too clever by looking
at f_free. [I could be convinced to go back to f_free = ULONG_MAX if
there are other instances of this.]

[1] https://github.com/ceph/ceph/pull/23323
[2] https://github.com/ceph/ceph/pull/23323#issuecomment-409249911

-- 
Patrick Donnelly
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