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Folks,
Create bottleneck when several clients are accessing a nfs volume.
On our setup:
Gluster 3.5.2 under centos7.
Hardware:
dual Xeon® CPU E5-2640
64GB RAM
SSD for rootfs
10Gb NIC
Context:
Around 700 nfs clients for small file or vm images.
The issue:
NFS client got intermittent hang (every minutes / for 10s each time). Even an “rpcinfo -t server nfs 3" will hang.
Gluster nfs process literally eat the CPU of the server
The cause:
the rmtab file located in /var/lib/glusterd/nfs/ is flushed from memory to /var/lib/glusterd/nfs/rmtab.tmp. During this time, NFS server hang literraly.
  Workaroud:
Move the file to memory for faster I/O using this option:
set nfs.mount-rmtab: /dev/shm/glusterfs.rmtab
Result:
We still have some hang but for ~300ms now, the load average of the server is WAY better.
Personal thought:
This feature is not usable and should be disabled by default.
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