Tuning the NFS Server

You may want to tune a server for optimal performance when you first set it up, and later, to improve performance in response to a specific problem.

Improving General Performance

Here are some general guidelines for improving the performance of your NFS server.

1. Measure the current level of performance for the network, server, and each client. See "Checking Network, Server, and Client Performance" on page 32.

2. Analyze the gathered data by graphing it. Look for exceptions, high disk and CPU utilization, and high disk service times. Apply thresholds or performance rules to the data.

3. Tune the server. See Chapter 4, "Configuring the Server and the Client to Maximize NFS Performance.

4. Repeat Steps 1 through 3 until you achieve the desired performance.

Resolving Performance Problems

Here are some general guidelines for resolving performance problems with your NFS server.

1. Use tools then observe the symptoms to pinpoint the source of the problem.

2. Measure the current level of performance for the network, server, and each client. See "Checking Network, Server, and Client Performance.

3. Analyze the data gathered by graphing the data. Look for exceptions, high disk and CPU utilization, and high disk service times. Apply thresholds or performance rules to the data.

4. Tune the server. See Chapter 4, "Configuring the Server and the Client to Maximize NFS Performance."

5. Repeat Steps 1 through 4 until you achieve the desired performance.

Checking Network, Server, and Client Performance

Before you can tune the NFS server, you must check the performance of the network, the NFS server, and each client. The first step is to check the performance of the network.

Checking the Network

If disks are operating normally, check network usage because a slow server and a slow network look the same to an NFS client.

Figure 3-1 illustrates the steps you must follow in sequence to check the network.

Figure 3-1

· To find the number of packets and collisions or errors on each network

1. Type netstat -i 15.

server% netstat -i 15 input le0 output input (Total) output packets errs packets errs colls packets errs packets errs colls 10798731 533 4868520 0 1078 24818184 555 14049209 157 894937 51 0 43 0 0 238 0 139 0 0 85 0 69 0 0 218 0 131 0 2 44 0 29 0 0 168 0 94 0 0

Use -I (Capital I) interface to look at other interfaces.

-i	Shows the state of the interfaces that are used for TCP/IP traffic
15	Collects information every 15 seconds

In the netstat -i 15 display, a machine with active network traffic should show both input packets and output packets continually increasing.

a. Calculate the network collision rate by dividing the number of output collision counts (Output Colls - le) by the number of output packets (le).

A network-wide collision rate greater than 10 percent can indicate an overloaded network, a poorly configured network, or hardware problems.

b. Calculate the input packet error rate by dividing the number of input errors (le) by the total number of input packets (le). If the input error rate is high (over 25 percent), the host may be dropping packets.

Other hardware on the network, as well as heavy traffic and low-level hardware problems, can introduce transmission problems. Bridges and routers can drop packets, forcing retransmissions and causing degraded performance.

Bridges also cause delays when they examine packet headers for Ethernet addresses. During these examinations, bridge network interfaces may drop packet fragments.

To compensate for bandwidth-limited network hardware:

• Reduce the packet size specifications.
• Set the read buffer size, rsize, and the write buffer size, wrsize, when using mount or in the /etc/vfstab file. Reduce the appropriate variable(s) (depending on the direction of data passing through the bridge) to 2048.

  If data passes in both directions through the bridge or other device, reduce both variables:

server:/home /home/server nfs rw,rsize=2048,wsize=2048 0 0

If a lot of read and write requests are dropped and the client is communicating with the server using the User Datagram Protocol (UDP), then the entire packet will be retransmitted, instead of the dropped packets.

· To determine how long a round trip echo packet takes on the network, and to display packet losses

* Type ping -sRv servername from the client to show the route taken by the packets.

If the round trip takes more than a few milliseconds (ms), there are slow routers on the network, or the network is very busy. Ignore the results from the first ping command.

client% ping -sRv servername PING server: 56 data bytes 64 bytes from server (129.145.72.15): icmp_seq=0. time=5. ms IP options: <record route> router (129.145.72.1), server (129.145.72.15), client (129.145.70.114), (End of record) 64 bytes from server (129.145.72.15): icmp_seq=1. time=2. ms IP options: <record route> router (129.145.72.1), server (129.145.72.15), client (129.145.70.114), (End of record)

s	Send option. Sends one datagram per second and prints one line of output for every echo response it receives. If there is no response, no output is produced.
R	Record route option. Sets the Internet Protocol (IP) record option that stores the route of the packet inside the IP header.
v	Verbose option. Lists any ICMP packets other than echo response that are received.

If you suspect a physical problem, use ping -sRv to find the response time of several hosts on the network. If the response time (ms) from one host is not what you would expect, investigate that host.

The ping command uses the ICMP protocol's echo request datagram to elicit an ICMP echo response from the specified host or network gateway. It can take a long time on a time-shared NFS server to obtain the ICMP echo. The distance from the client to the NFS server is a factor for how long it takes to obtain the ICMP echo from the server.

Figure 3-2 shows the possible responses or the lack of response to the ping -sRv command.

Figure 3-2 ping -sRv

Checking the NFS Server

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Note - The server used in the following examples is a large SPARCserver 690 configuration.

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Figure 3-3, which follows, illustrates the steps you must follow in sequence to check the NFS server.

Figure 3-3

· To see what is being exported

* Type share.

server% share - /export/home rw=netgroup "" - /var/mail rw=netgroup "" - /cdrom/solaris_2_3_ab ro ""

· To display the file systems mounted and the disk drive on which the file system is mounted

* Type df -k. If an file system is over 100 percent full, it may cause NFS write errors on the clients.

server% df -k Filesystem kbytes used avail capacity Mounted on /dev/dsk/c1t0d0s0 73097 36739 29058 56% / /dev/dsk/c1t0d0s3 214638 159948 33230 83% /usr /proc 0 0 0 0% /proc fd 0 0 0 0% /dev/fd swap 501684 32 501652 0% /tmp /dev/dsk/c1t0d0s4 582128 302556 267930 53% /var/mail /dev/md/dsk/d100 7299223 687386 279377 96% /export/home /vol/dev/dsk/c0t6/solaris_2_3_ab 113512 113514 0 100% /cdrom/solaris_2_3_ab

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Note - For this example, the /var/mail and /export/home file systems are used.

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Determine on which disk the file systems returned by the df -k command are stored

In the previous example, you'll note that /var/mail is stored on /dev/dsk/c1t0d0s4 and /export/home is stored on /dev/md/dsk/d100, an Online: DiskSuite^(TM) metadisk.

· If an Online: DiskSuite metadisk is returned by the df -k command, determine the number of the disk

* Type /usr/opt/SUNWmd/sbin/metastat <disknumber>. In the previous example, /usr/opt/SUNWmd/sbin/metastat d100 determines what physical disk /dev/md/dsk/d100 uses.

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Note - The d100 disk is a mirrored disk. Each mirror is made up of three striped disks of one size concatenated with four striped disks of another size. There is also a hot spare disk. This system uses IPI disks, idX. SCSI disks, sdX, are treated identically.

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server% /usr/opt/SUNWmd/sbin/metastat d100 d100: metamirror Submirror 0: d10 State: Okay Submirror 1: d20 State: Okay Regions which are dirty: 0% Pass = 1 Read option = round-robin (default) Write option = parallel (default) Size: 15536742 blocks d10: Submirror of d100 State: Okay Hot spare pool: hsp001 Size: 15536742 blocks Stripe 0: (interlace : 96 blocks) Device Start Block Dbase State Hot Spare /dev/dsk/c1t1d0s7 0 No Okay /dev/dsk/c2t2d0s7 0 No Okay /dev/dsk/c1t3d0s7 0 No Okay Stripe 1: (interlace : 64 blocks) Device Start Block Dbase State Hot Spare /dev/dsk/c3t1d0s7 0 No Okay /dev/dsk/c4t2d0s7 0 No Okay /dev/dsk/c3t3d0s7 0 No Okay /dev/dsk/c4t4d0s7 0 No Okay d20: Submirror of d100 State: Okay Hot spare pool: hsp001 Size: 15536742 blocks Stripe 0: (interlace : 96 blocks) Device Start Block Dbase State Hot Spare /dev/dsk/c2t1d0s7 0 No Okay /dev/dsk/c1t2d0s7 0 No Okay /dev/dsk/c2t3d0s7 0 No Okay Stripe 1: (interlace : 64 blocks) Device Start Block Dbase State Hot Spare /dev/dsk/c4t1d0s7 0 No Okay /dev/dsk/c3t2d0s7 0 No Okay /dev/dsk/c4t3d0s7 0 No Okay /dev/dsk/c3t4d0s7 0 No Okay /dev/dsk/c2t4d0s7

· To determine the /dev/dsk entries for each exported file system

Use the whatdev script to find the instance or nickname for the drive or type ls -lL /dev/dsk/c1t0d0s4 and more /etc/path_to_inst to find the /dev/dsk entries.

Follow either procedure in sections "Using the whatdev Script" or "Using ls -lL to Identify /dev/dsk Entries."

Using the whatdev Script

a. Type the whatdev script using a text editor.

#!/bin/csh # print out the drive name - st0 or sd0 - given the /dev entry # first get something like "/iommu/.../.../sd@0,0" set dev = `/bin/ls -l $1 | nawk '{ n = split($11, a, "/"); split(a[n],b,":"); for(i = 4; i < n; i++) printf("/%s",a[i]); printf("/%s\n", b[1]) }'` if ( $dev == "" ) exit # then get the instance number and concatenate with the "sd" nawk -v dev=$dev '$1 ~ dev { n = split(dev, a, "/"); split(a[n], \ b, "@"); printf("%s%s\n", b[1], $2) }' /etc/path_to_inst

b. Determine the /dev/dsk entry for the file system by typing df /<filesystemname>.

In this example you would type df /var/mail.

furious% df /var/mail Filesystem kbytes used avail capacity Mounted on /dev/dsk/c1t0d0s4 582128 302556 267930 53% /var/mail

c. Determine the disk number by typing whatdev diskname (the disk name returned by the df /<filesystemname> command).

In this example you would type whatdev /dev/dsk/c1t0d0s4.

Disk number id8 is returned. This is IPI disk 8.

server% whatdev /dev/dsk/c1t0d0s4 id8

d. Repeat steps b and c for each file system not stored on a metadisk (dev/md/dsk).

e. If the file system is stored on a meta disk, (dev/md/dsk), look at the metastat output and run the whatdev script on all drives included in the metadisk.

In this example type whatdev /dev/dsk/c2t1d0s7.

There are 14 disks in the /export/home file system. Running the whatdev script on the /dev/dsk/c2t1d0s7 disk, one of the 14 disks comprising the /export/home file system, returns the following display.

server% whatdev /dev/dsk/c2t1d0s7 id17

Note that /dev/dsk/c2t1d0s7 is disk id17. This is IPI disk 17.

f. Go to the procedure "To see the disk statistics for each disk" on page 44."

Using ls -lL to Identify /dev/dsk Entries

If you followed the procedure "Using the whatdev Script" skip this section. Go to the procedure "To see the disk statistics for each disk."

If you did not follow the procedure outlined in"Using the whatdev Script:"

a. List the drive and its major and minor device numbers by typing

ls -lL <disknumber>. For example, for the /var/mail file system, type: ls -lL /dev/dsk/c1t0d0s4.

ls -lL /dev/dsk/c1t0d0s4 brw-r----- 1 root 66, 68 Dec 22 21:51 /dev/dsk/c1t0d0s4

b. Locate the minor device number in the ls -lL output. In the previous screen example, the first number following the file ownership (root), 66, is the major number. The second number, 68, is the minor device number.

c. Determine the disk number.

Divide the minor device number, 68 in the previous example, by 8.

Disk number -- 68/8 = 8.5

Truncate the fraction. The number, 8, is the disk number.

d. Determine the slice (partition) number.

Look at the number following the s (for slice) in the disk number. For example, in /dev/dsk/c1t0d0s4, the 4 following the s refers to slice 4.

Now you know that the disk number is 8 and the slice number is 4. This disk is either sd8 (SCSI) or ip8 (IPI).

e. Go to the procedure, "To see the disk statistics for each disk," which follows.

· To see the disk statistics for each disk

* Type iostat -x 15.

The -x option supplies extended disk statistics. The 15 means disk statistics are gathered every 15 seconds.

server% iostat -x 15 extended disk statistics disk r/s w/s Kr/s Kw/s wait actv svc_t %w %b id10 0.1 0.2 0.4 1.0 0.0 0.0 24.1 0 1 id11 0.1 0.2 0.4 0.9 0.0 0.0 24.5 0 1 id17 0.1 0.2 0.4 1.0 0.0 0.0 31.1 0 1 id18 0.1 0.2 0.4 1.0 0.0 0.0 24.6 0 1 id19 0.1 0.2 0.4 0.9 0.0 0.0 24.8 0 1 id20 0.0 0.0 0.1 0.3 0.0 0.0 25.4 0 0 id25 0.0 0.0 0.1 0.2 0.0 0.0 31.0 0 0 id26 0.0 0.0 0.1 0.2 0.0 0.0 30.9 0 0 id27 0.0 0.0 0.1 0.3 0.0 0.0 31.6 0 0 id28 0.0 0.0 0.0 0.0 0.0 0.0 5.1 0 0 id33 0.0 0.0 0.1 0.2 0.0 0.0 36.1 0 0 id34 0.0 0.2 0.1 0.3 0.0 0.0 25.3 0 1 id35 0.0 0.2 0.1 0.4 0.0 0.0 26.5 0 1 id36 0.0 0.0 0.1 0.3 0.0 0.0 35.6 0 0 id8 0.0 0.1 0.2 0.7 0.0 0.0 47.8 0 0 id9 0.1 0.2 0.4 1.0 0.0 0.0 24.8 0 1 sd15 0.1 0.1 0.3 0.5 0.0 0.0 84.4 0 0 sd16 0.1 0.1 0.3 0.5 0.0 0.0 93.0 0 0 sd17 0.1 0.1 0.3 0.5 0.0 0.0 79.7 0 0 sd18 0.1 0.1 0.3 0.5 0.0 0.0 95.3 0 0 sd6 0.0 0.0 0.0 0.0 0.0 0.0 109.1 0 0

Use the iostat -x 15 command to see the disk number for the extended disk statistics. In the next procedure you will use a sed script to translate the disk names into disk numbers.

The output for the extended disk statistics is:

r/s	Reads per second
w/s	Writes per second
Kr/s	Kbytes read per second
Kw/s	Kbytes written per second
wait	Average number of transactions waiting for service (queue length)
actv	Average number of transactions actively being serviced
svc_t	Average service time, (milliseconds)
%w	Percentage of time the queue is not empty
%b	Percentage of time the disk is busy

· To translate disk names into disk numbers

Use iostat and sar. One quick way to do this is to use a sed script:.

1. Type in a sed script using a text editor similar to the following d2fs.server sed script.

   Your sed script should substitute the file system name for the disk number.

   In this example, disk id8 is substituted for /var/mail and disks id9,

  id10, id11, id17, id18, id19, id25, id26, id27, id28,
  id33, id34, id35, and id36 are substituted for /export/home.

sed 's/id8 /var/mail/ s/id9 /export/home/ s/id10 /export/home/ s/id11 /export/home/ s/id17 /export/home/ s/id18 /export/home/ s/id25 /export/home/ s/id26 /export/home/ s/id27 /export/home/ s/id28 /export/home/ s/id33 /export/home/ s/id34 /export/home/ s/id35 /export/home/ s/id36 /export/home/'

2. Run the iostat -xc 15 command through the sed script by typing iostat -xc 15 | d2fs.server.

The options to the previous iostat -xc 15 | d2fs.server command are explained below.

-x	Supplies extended disk statistics
-c	Reports the percentage of time the system was in user mode (us), system mode (sy), waiting for I/O (wt), and idling (id)
15	Means disk statistics are gathered every 15 seconds

Code Example 3-1 Output for the iostat -xc 15 Command

% iostat -xc 15 | d2fs.server extended disk statistics cpu disk r/s w/s Kr/s Kw/s wait actv svc_t %w %b us sy wt id export/home 0.1 0.2 0.4 1.0 0.0 0.0 24.1 0 1 0 11 2 86 export/home 0.1 0.2 0.4 0.9 0.0 0.0 24.5 0 1 export/home 0.1 0.2 0.4 1.0 0.0 0.0 31.1 0 1 export/home 0.1 0.2 0.4 1.0 0.0 0.0 24.6 0 1 export/home 0.1 0.2 0.4 0.9 0.0 0.0 24.8 0 1 id20 0.0 0.0 0.1 0.3 0.0 0.0 25.4 0 0 export/home 0.0 0.0 0.1 0.2 0.0 0.0 31.0 0 0 export/home 0.0 0.0 0.1 0.2 0.0 0.0 30.9 0 0 export/home 0.0 0.0 0.1 0.3 0.0 0.0 31.6 0 0 export/home 0.0 0.0 0.0 0.0 0.0 0.0 5.1 0 0 export/home 0.0 0.0 0.1 0.2 0.0 0.0 36.1 0 0 export/home 0.0 0.2 0.1 0.3 0.0 0.0 25.3 0 1 export/home 0.0 0.2 0.1 0.4 0.0 0.0 26.5 0 1 export/home 0.0 0.0 0.1 0.3 0.0 0.0 35.6 0 0 var/mail 0.0 0.1 0.2 0.7 0.0 0.0 47.8 0 0 id9 0.1 0.2 0.4 1.0 0.0 0.0 24.8 0 1 sd15 0.1 0.1 0.3 0.5 0.0 0.0 84.4 0 0 sd16 0.1 0.1 0.3 0.5 0.0 0.0 93.0 0 0 sd17 0.1 0.1 0.3 0.5 0.0 0.0 79.7 0 0 sd18 0.1 0.1 0.3 0.5 0.0 0.0 95.3 0 0 sd6 0.0 0.0 0.0 0.0 0.0 0.0 109.1 0 0

The following terms and abbreviations explain the output and headings of Code Example 3-1.

disk	Name of disk device
r/s	Average read operations per second
w/s	Average write operations per second

Kr/s	Average Kbytes read per second
Kw/s	Average Kbytes written per second
wait	Number of requests outstanding in the device driver queue
actv	Number of requests active in the disk hardware queue
%w	Occupancy of the wait queue
%b	Occupancy of the active queue--device busy
svc_t	Average service time in milliseconds for a complete disk request; includes wait time, active queue time, seek rotation, and transfer latency
us	CPU time
sy	System time
wt	Wait for I/O time
id	Idle time

3. Run the sar -d 15 1000 command through the sed script by typing sar -d 15 1000 | d2fs.server.

Code Example 3-2 Output of the sar -d 15 1000 | d2fs.server Command

server% sar -d 15 1000 | d2fs.server 12:44:17 device %busy avque r+w/s blks/s avwait avserv 12:44:18 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 id20 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 var/mail 0 0.0 0 0 0.0 0.0 export/home 0 0.0 0 0 0.0 0.0 sd15 7 0.1 4 127 0.0 17.6 sd16 6 0.1 3 174 0.0 21.6 sd17 5 0.0 3 127 0.0 15.5

The sar -d option reports the activities of the disk devices. The 15 means that data is collected every 15 seconds. The 1000 means that data is collected 1000 times. The following terms and abbreviations explain the output and headings of Code Example 3-2.

device	Name of the disk device being monitored
%busy	Percentage of time the device spent servicing a transfer request (same as iostat %b)
avque	Average number of requests outstanding during the monitored period (measured only when the queue was occupied) (same as iostat actv)
r+w/s	Number of read and write transfers to the device,
blks/s	Number of 512-byte blocks transferred to the device,
avwait	Average time, in milliseconds, that transfer requests wait idly in the queue (measured only when the queue is occupied) (iostat wait gives the length of this queue)
avserv	Average time, in milliseconds, for a transfer request to be completed by the device (for disks, this includes seek, rotational latency, and data transfer times)

4. For file systems that are exported via NFS, check the %b/%busy value. If it is more than 30%, check the svc_t value.

   The %b value, the percentage of time the disk is busy, is returned by the iostat command. The %busy value, the percentage of time the device spent servicing a transfer request, is returned by the sar command. If the %b and the %busy values are greater than 30 percent, go to Step 5. Otherwise, go on to "To collect data on a regular basis," which follows.

5. Calculate the svc_t/(avserv + avwait) value. The svc_t value, the average service time in milliseconds, is returned by the iostat command. The avserv value, the average time (milliseconds) for a transfer request to be completed by the device, is returned by the sar command. Add the avwait to get the same measure as svc_t.

   If the svc_t value, the average total service time in milliseconds, is more than 40 ms, the disk is taking a long time to respond. An NFS request with disk I/O will appear to be slow by the NFS clients. The NFS response time

should be less than 50 ms on average, to allow for NFS protocol processing and network transmission time. The disk response should be less than 40 ms.

The average service time in milliseconds is a function of the disk. If you have fast disks, the average service time should be less than if you have slow disks.

· To collect data on a regular basis

* Uncomment the lines in the user's sys crontab file so that sar collects the data for one month.

root# crontab -l sys #ident"@(#)sys1.592/07/14 SMI"/* SVr4.0 1.2*/ # # The sys crontab should be used to do performance collection. # See cron and performance manual pages for details on startup. 0 * * * 0-6 /usr/lib/sa/sa1 20,40 8-17 * * 1-5 /usr/lib/sa/sa1 5 18 * * 1-5 /usr/lib/sa/sa2 -s 8:00 -e 18:01 -i 1200 -A

Performance data will be continuously collected to provide you with a history of sar results.

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Note - A few hundred Kbytes will be used at most in /var/adm/sa.

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· To spread the load out over the disks

• Use Solstice^(TM) DiskSuite or Online: DiskSuite to stripe the file system over multiple disks if the disks are overloaded.
• Use a Prestoserve write cache to reduce the number of accesses and spread peak access loads out in time.

  See the section "Using Solstice DiskSuite or Online: DiskSuite to Spread Disk Access Load" on page 67 in Chapter 4.

· To adjust the buffer cache if you have read-only file systems

* Increase the buffer cache.

See "Adjusting the Buffer Cache: bufhwm" on page 80 in Chapter 4.

· To identify NFS problems, display server statistics

* Type nfsstat -s (see Code Example 3-3.) The -s option displays server statistics.

Code Example 3-3 Using the nfsstat -s Command to Display Server Statistics

server% nfsstat -s Server rpc: calls badcalls nullrecv badlen xdrcall 480421 0 0 0 0 Server nfs: calls badcalls 480421 2 null getattr setattr root lookup readlink read 95 0% 140354 29% 10782 2% 0 0% 110489 23% 286 0% 63095 13% wrcache write create remove rename link symlink 0 0% 139865 29% 7188 1% 2140 0% 91 0% 19 0% 231 0% mkdir rmdir readdir statfs 435 0% 127 0% 2514 1% 2710 1%

The NFS server display shows the number of NFS calls received (calls) and rejected (badcalls), and the counts and percentages for the various calls that were made. The number and percentage of calls returned by the nfsstat -s command are described in Table 3-2 on page 54.

The following terms explain the headings in the output of Code Example 3-3.

calls	Total number of RPC calls received
badcalls	Total number of calls rejected by the RPC layer
nullrecv	Number of times an RPC call was not available when it was thought to be received

badlen	Number of RPC calls with a length shorter than a minimum-sized RPC call
xdrcall	Number of RPC calls whose header could not be XDR decoded

Table 3-1 explains the nfsstat -s command output and what actions to take.

Table 3-1 nfsstat -s

If	Then
writes > 5%**	Install a Prestoserve NFS accelerator (SBus card or NVRAM-NVSIMM) for peak performance. See the section "Prestoserve NFS Accelerator" on page 75 in Chapter 4.
There are any badcalls	Badcalls are calls rejected by the RPC layer and are the sum of badlen and xdrcall. The network may be overloaded. Identify an overloaded network using network interface statistics.
readlink > 10% of total lookup calls on NFS servers	NFS clients are using excessive symbolic links that are on the file systems exported by the server. Replace the symbolic link with a directory. Mount both the underlying file system and the symbolic link's target on the NFS client. See the procedure that follows "To eliminate symbolic links" on page 52.
getattr > 40%	Increase the client attribute cache using the actimeo option. Make sure that the DNLC and inode caches are large. Use vmstat -s to determine the percent hit rate (cache hits) for the DNLC and if needed increase ncsize in the /etc/system file. See the procedure "To show the Directory Name Lookup Cache (DNLC) hit rate," in this chapter and the section "Directory Name Lookup Cache (DNLC)" on page 82 in Chapter 4.
** The number of writes, 29% in the previous example, is very high.

· To eliminate symbolic links

If symlink is greater than 10 percent in the output of the nfsstat -s command (see Code Example 3-3), eliminate symbolic links. In the following example, /usr/tools/dist/sun4 is a symbolic link for /usr/dist/bin.

1. Type rm /usr/dist/bin to eliminate the symbolic link for /usr/dist/bin.

# rm /usr/dist/bin

2. Type mkdir /usr/dist/bin to make /usr/dist/bin a directory.

# mkdir /usr/dist/bin

3. Mount the directories and type:

client# mount server: /usr/dist/bin client# mount server: /usr/tools/dist/sun4 client# mount

· To show the Directory Name Lookup Cache (DNLC) hit rate

1. Type vmstat -s.

   This command returns the hit rate (cache hits).

% vmstat -s ... lines omitted 79062 total name lookups (cache hits 94%) 16 toolong

2. If the hit rate is less than 90 percent and there is no problem with the number of longnames, increase the variable, ncsize, in the /etc/system file:

set ncsize=5000

Directory names less than 30 characters long are cached and names that are too long to be cached are also reported.

The default value of ncsize is:

ncsize (name cache) = 17 * maxusers + 90

• For NFS server benchmarks ncsize has been set as high as 16000.
• For maxusers = 2048 ncsize would be set at 34906.

For more information on the Directory Name Lookup Cache, see "Directory Name Lookup Cache (DNLC)" on page 82 in Chapter 4.

3. Reboot the system.

· To check the system state if the system has a Prestoserve NFS accelerator

* Type /usr/sbin/presto. Verify that it is in the UP state.

server% /usr/sbin/presto state = UP, size = 0xfff80 bytes statistics interval: 1 day, 23:17:50 (170270 seconds) write cache efficiency: 65% All 2 batteries are ok

• If it is in the DOWN state, type presto -u.

server% presto -u

• If it is in the error state, see the Prestoserve User's Guide.

Table 3-2 describes the NFS operations and their functions.

Table 3-2

Operation	Function
create	Creates a file system node; may be a file or symbolic link
statfs	Gets dynamic file system information
getattr	Gets file/directory attributes such as file type, size, permissions, and access times
link	Creates a hard link in the remote file system
lookup	Searches directory for file and return file handle
mkdir	Creates a directory
null	Does nothing; used for testing and timing of server response
read	Reads an 8-KByte block of data
readdir	Reads a directory entry
readlink	Follows a symbolic link on the server
rename	Changes the file's directory name entry
remove	Removes a file system node
rmdir	Removes a directory
root	Retrieves the root of the remote file system (not presently used)
setattr	Changes file or directory attributes
symlink	Makes a symbolic link in a remote file system
wrcache	Writes an 8 Kbyte block of data to the remote cache (not presently used)
write	Writes an 8 Kbyte block of data

Checking Each Client

The overall tuning process must include client tuning. Sometimes, tuning the client yields more improvement than fixing the server. For example, adding 4 Mbytes of memory to each of 100 clients dramatically decreases the load on an NFS server.

Following is an overview of the steps to check each client. These steps will be discussed in the following procedures:

1. Check the client statistics to see if the client is having NFS problems.

2. Display statistics for each NFS mounted file system.

· To check the client statistics to see if the client is having NFS problems

* Type nfsstat -c at the % prompt (see Code Example 3-4). Look for errors and retransmits

Code Example 3-4 Output of the nfsstat -c Command

client % nfsstat -c Client rpc: calls badcalls retrans badxids timeouts waits newcreds 384687 1 52 7 52 0 0 badverfs timers toobig nomem cantsend bufulocks 0 384 0 0 0 0 Client nfs: calls badcalls clgets cltoomany 379496 0 379558 0 Version 2: (379599 calls) null getattr setattr root lookup readlink read 0 0% 178150 46% 614 0% 0 0% 39852 10% 28 0% 89617 23% wrcache write create remove rename link symlink 0 0% 56078 14% 1183 0% 1175 0% 71 0% 51 0% 0 0% mkdir rmdir readdir statfs 49 0% 0 0% 987 0% 11744 3%

The output of Code Example 3-4 shows that there were only 52 retransmits (retrans ) and 52 time-outs (timeout) out of 384687 calls.

The nfsstat -c display in Code Example 3-4 shows the following fields:

calls	Total number of calls sent
badcalls	Total number of calls rejected by RPC
retrans	Total number of retransmissions
badxid	Number of times that a duplicate acknowledgment was received for a single NFS request
timeout	Number of calls that timed out

wait	Number of times a call had to wait because no client handle was available
newcred	Number of times the authentication information had to be refreshed

Table 3-2, shown earlier in this chapter, describes the NFS operations. Table 3-3 explains the output of the nfsstat -c command and what action to take.

Table 3-3 nfsstat -c

If	Then
retrans > 5% of the calls	The requests are not reaching the server.
badxid is approximately equal to badcalls	The network is slow. Consider installing a faster network or installing subnets.
badxid is approximately equal to timeouts	Most requests are reaching the server but the server is slower than expected. Watch expected times using nfsstat -m.
badxid is close to 0	The network is dropping requests. Reduce rsize and wsize in the mount options.
null > 0	A large amount of null calls suggests that the automounter is retrying the mount frequently. The timeout values for the mount are too short. Increase the mount timeout parameter, timeo, on the automounter command line

The third-party tools you can use for NFS/networks include:

• NetMetrix (Hewlett-Packard)
• SharpShooter (AIM Technology)

· To display statistics for each NFS mounted file system

* Type nfsstat -m. The statistics include the server name and address, mount flags, current read and write sizes, transmission count, and the timers used for dynamic transmission.

client % nfsstat -m /export/home from server:/export/home Flags: vers=2,hard,intr,dynamic,rsize=8192,wsize=8192,retrans=5 Lookups: srtt=10 (25ms), dev=4 (20ms), cur=3 (60ms) Reads: srtt=9 (22ms), dev=7 (35ms), cur=4 (80ms) Writes: srtt=7 (17ms), dev=3 (15ms), cur=2 (40ms) All: srtt=11 (27ms), dev=4 (20ms), cur=3 (60ms)

The following terms, used In the output of the nfsstat -m command, are explained below:

srtt	Smoothed round-trip time
dev	Estimated deviation
cur	Current backed-off timeout value

The numbers in parentheses are the actual times in milliseconds. The other values are unscaled values kept by the operating system kernel. You can ignore the unscaled values. Response times are shown for lookups, reads, writes, and a combination of all of these operations (all). Table 3-4 shows the appropriate action for the nfsstat -m command.

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Note - These statistics are only generated for NFS over UDP (the default for Version 2.) NFS over TCP does not need retransmit timers and is the default for Version 3.

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Table 3-4 nfsstat -m

If	Then
srtt > 50 ms	That mount point is slow. Check the network and the server for the disk(s) that provide that mount point. See the steps earlier in this chapter.
You the message "NFS server not responding" is displayed	Try increasing the timeo parameter in the /etc/vfstab file to eliminate the messages and improve performance. Doubling the initial timeo parameter value is a good baseline. After changing the timeo value in the vfstab file, invoke the nfsstat -c command and observe the badxid value returned by the command. Follow the recommendations for the nfsstat -c command earlier in this section.
Lookups: cur > 80 ms	The requests are taking too long to process. This indicates a slow network or a slow server.
Reads: cur > 150 ms	The requests are taking too long to process. This indicates a slow network or a slow server.
Writes: cur > 250 ms	The requests are taking too long to process. This indicates a slow network or a slow server.