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Recently, Bill Broadley of UC Davis presented the Beowulf mailing list with a survey on NFS and HPC. Bill has collected the results and given permission to post a summary on Cluster Monkey. Many thanks for all the 27 respondents (who are seasoned HPC administrators) . Note that not all respondents answered all questions..

1) cluster OS:

  • 72% Redhat/CentOS/Scientific linux or derivative
  • 24% Debian/Ubuntu or derivative
  • 4% SUSE or derivative

2) Appliance/NAS or linux server

  • 32% NFS appliance
  • 76% linux server
  • 12% other (illumos/Solaris)

3) Appliances used (one each, free form answers):

  • Hitachi BlueARC, EMC Isilon, DDN/GPFS, x4540
  • Not sure - something that corporate provided. An F5, maybe...? Also a
  • Panasas system for /scratch.
  • NetApp FAS6xxx
  • netapp
  • isilon x and nl
  • Isilon
  • NetApp
  • Synology

4) Which kernel do you use:

  • 88% one provided with the linux distribution
  • 12% one that I compile/tweak myself

5) what kernel changes do you make

  • CPU performance tweaking, network performance.
  • raise ARP cache size, newer kernel than stock 3.2 was needed for newer
  • hardware 3.14 at the moment
  • ZFS

6) Do you often see problems like nfs: server 192.168.5.30 not responding, timed out:

  • 42.3% Never
  • 23.1% Sometimes
  • 19.2% rarely
  • 7.7% daily
  • 7.7% often

7) If you see NFS time outs what do you do (free form answers)

  • nothing
  • nothing
  • Restart NFSd, look for performance intensive jobs, sometimes increase NFSd.
  • Look at what's going on on that server. That means looking at what the> disks are doing, what network flows are going to/from that server and determine if the load is something to take action on or to let.
  • Not much
  • Reboot
  • Resolve connectivity issue if any and run mount command on nodes. If this doesn't fix it, then reboot.
  • Ignore them, unless they become a problem.
  • Look for the root cause of the issue, typically system is suffering network issues or is overloaded by a user 'abuse/missuse'.
  • diagnose and identify underlying cause
  • Try to figure out who is overloading the NFS server (hard job)
  • Troubleshoot, typically a machine is offline or network saturation

8) which NFS options do you use (free form):

  • tcp,async,nodev,nosuid,rsize=32768,wsize=32768,timeout=10
  • nfsvers=3,nolock,hard,intr,timeo=16,retrans=8
  • hard,intr,rsize=32768,wsize=32768
  • all default
  • async
  • async,nodev,nosuid,rsize=32768,wsize=32768
  • tcp,async, nodev, nosuid,timeout=10
  • -rw,intr,nosuid,proto=tcp (mostly. Could be "ro" and/or "suid")
  • rsize=32768,wsize=32768,hard,intr,vers=3,proto=tcp,retrans=2,timeo=600
  • rsize=32768,wsize=32768
  • -nobrowse,intr,rsize=32768,wsize=32768,vers=3
  • udp,hard,timeo=50,retrans=7,intr,bg,rsize=8192,wsize=8192,nfsvers=3, mountvers=3
  • RHEL defaults
  • default ones, they're almost always the best ones
  • rw,nosuid,nodev,tcp,hard,intr,vers=4
  • rw,relatime,vers=4.0,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp, port=0,timeo=600,retrans=2,sec=sys, clientaddr=10.5.6.7,local_lock=none, addr=10.5.6.1
  • defaults, netdev,vers=3
  • nfsvers=3,tcp,rw,hard,intr,timeo=600,retrans=2
  • rw,hard,tcp,nfsvers=3,noacl,nolock
  • default rhel6 (+nosuid, nodev, and sometimes nfsver=3)
  • tcp, intr, noauto, timeout, rsize, wsize, auto
  • nfsvers=3,rsize=1024,wsize=1024,cto

9) Any explanations:

  • We have not yet made the change to nfsv4, we use nolock due to various application "issues", we do not hard set rsize/wsize as they have been negotiating better values for a number of years on their own under v3, and the timeout/retrans are a bit of a legacy set of values from working on this issue of server overload. Hard was a choice on our end to pick that having things hang definitely seemed better then having things fail and go stale. We still agree with the choice of hard. Intr just helps to "interupt" stuck things when needed.
  • We like to be able to ctrl-C hung processes. For some systems we use larger rsize/wsize if the vendor supports it.
  • works for me without tewaks
  • We didn't use tcp until the last couple of years.
  • Probably needs a revisit- block size was set up for 2.x series kernels
  • default of centos 7
  • nfsv4 was not stable enough last time out, don't fix rsize/wsize as client/server usually negotiate to 1M anyway
  • We have frequent power outage (5+ times a year) and noauto helps our not to hang on mounting nfs shares. Drawback is you have to manually mount. Time out helps with this issue as well.
  • These are adjusted if necessary for particular workloads

10) what parts of the file system do you use NFS for (free form):

  • /home
  • /home
  • /home
  • /home
  • /home
  • /home
  • /home
  • /home and /apps
  • We use NFS for the OS (NFSRoot), App tree, $HOME, Group dedicated space, as well as some of our scratch spaces. All of these come from different NFS servers.
  • /home, /apps
  • /home /opt /etc /usr /boot
  • /home,/apps,
  • /home, /apps, /scratch - all of 'em
  • /home, long term project storage, shared software
  • /cluster/home,/cluster/local,/cluster/scratch,/cluster/data
  • home, apps, shared data
  • /usr/local, /home
  • /home , /apps
  • various
  • /home, /group, /usr/local
  • /home, parts of /opt, some specific top level auto-mountable dirs
  • What above is called /apps and /home for a few medium sized systems
  • /home, /local, /opt, /diskless
  • /home, /opt, diskless node images

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