Automounting NFS over RDMA fails

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 6.3
  • kernel 2.6.32-279.14.1.el6
  • autofs-5.0.5-55.el6_3

Issue

  • Automounting NFS over RDMA fails.
  • Directly mounting an NFS share via RDMA functions as desired.

Resolution

Workaround

  • Set the MOUNT_WAIT parameter in /etc/sysconfig/autofs to a value of 40:
MOUNT_WAIT=40

Root Cause

  • In Red Hat Enterprise Linux 6.2 autofs does not do any probing of single mount entries, however in 6.3 autofs now probes latency even in single host entry cases. This probing of latency causes problems with RDMA as autofs does not probe RDMA but only TCP/UDP, this causes the probe to fail thus causing autofs to fail to mount the host entry.

  • Setting the MOUNT_WAIT parameter to 40 effectively disables the probing functionality described above, as the recent changes to autofs check to see if default_get_mount_wait is equal to -1. Since the modification of MOUNT_WAIT makes this value non-equal to -1 the probing stops.

Diagnostic Steps

  • Enable autofs debugging by editing the /etc/sysconfig/autofs file and modifying the OPTIONS= directive with the following:
OPTIONS="--debug"
  • Reproduce the problem and investigate /var/log/messages for the following messages, note the get_nfs_info calls on both the TCP/UDP protocols but not RDMA:
sun_mount: parse(sun): mounting root /home, mountpoint hostname, what server.example.com:/share, fstype nfs, options nfsvers=4,rdma,port=2050,rw,nosuid,softq
mount_mount: mount(nfs): root=/home name=hostname what=server.example.com:/share, fstype=nfs, options=nfsvers=4,rdma,port=2050,rw,nosuid,softq
mount_mount: mount(nfs): nfs options="nfsvers=4,rdma,port=2050,rw,nosuid,softq", nosymlink=0, ro=0
get_nfs_info: called with host hostname(192.168.8.13) proto tcp version 0x70
get_nfs_info: called with host hostname(192.168.8.13) proto udp version 0x70
mount(nfs): no hosts available

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