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Chapter 8. Monitoring pNFS SCSI layouts functionality

You can monitor if the pNFS client and server exchange proper pNFS SCSI operations or if they fall back on regular NFS operations.

Prerequisites

  • A pNFS SCSI client and server are configured.

8.1. Checking pNFS SCSI operations from the server using nfsstat

This procedure uses the nfsstat utility to monitor pNFS SCSI operations from the server.

Procedure

  1. Monitor the operations serviced from the server: 

    # watch --differences \
        "nfsstat --server | egrep --after-context=1 read\|write\|layout"

Every 2.0s: nfsstat --server | egrep --after-context=1 read\|write\|layout

putrootfh    read         readdir      readlink     remove	 rename
2         0% 0         0% 1         0% 0         0% 0         0% 0         0%
--
setcltidconf verify	  write        rellockowner bc_ctl	 bind_conn
0         0% 0         0% 0         0% 0         0% 0         0% 0         0%
--
getdevlist   layoutcommit layoutget    layoutreturn secinfononam sequence
0         0% 29        1% 49        1% 5         0% 0         0% 2435     86%

  2. The client and server use pNFS SCSI operations when:

    • The layoutget, layoutreturn, and layoutcommit counters increment. This means that the server is serving layouts.
    • The server read and write counters do not increment. This means that the clients are performing I/O requests directly to the SCSI devices.

8.2. Checking pNFS SCSI operations from the client using mountstats

This procedure uses the /proc/self/mountstats file to monitor pNFS SCSI operations from the client.

Procedure

  1. List the per-mount operation counters: 

    # cat /proc/self/mountstats \
      | awk /scsi_lun_0/,/^$/ \
      | egrep device\|READ\|WRITE\|LAYOUT

device 192.168.122.73:/exports/scsi_lun_0 mounted on /mnt/rhel7/scsi_lun_0 with fstype nfs4 statvers=1.1
    nfsv4:  bm0=0xfdffbfff,bm1=0x40f9be3e,bm2=0x803,acl=0x3,sessions,pnfs=LAYOUT_SCSI
            READ: 0 0 0 0 0 0 0 0
           WRITE: 0 0 0 0 0 0 0 0
        READLINK: 0 0 0 0 0 0 0 0
         READDIR: 0 0 0 0 0 0 0 0
       LAYOUTGET: 49 49 0 11172 9604 2 19448 19454
    LAYOUTCOMMIT: 28 28 0 7776 4808 0 24719 24722
    LAYOUTRETURN: 0 0 0 0 0 0 0 0
     LAYOUTSTATS: 0 0 0 0 0 0 0 0

  2. In the results:

    • The LAYOUT statistics indicate requests where the client and server use pNFS SCSI operations.
    • The READ and WRITE statistics indicate requests where the client and server fall back to NFS operations.