Troubleshooting

5

Table 5-1 lists actions to perform when you encounter a tuning problem.

Table 5-1

Command/Tool	If the Command Output Is	Then
netstat -i	Collis+Ierrs+Oerrs/Ipkts + Opkts > 2%	Check Ethernet hardware.
netstat -i	Collis/Opkts > 10%	Add Ethernet interface and distribute client load.
netsat -i	Ierrs/Ipks > 25%	High input error rate. The host may be dropping packets. To compensate for bandwidth-limited network hardware: reduce the packet size, set the read buffer size, rsize, and/or the write buffer size, wsize, when using mount or in the /etc/vfstab file to 2048. See the procedure "To find the number of packets and collisions/errors on each network" in Chapter 3, "Analyzing NFS Performance."
nfsstat -s	readlink > 10%	Replace symbolic links with mount points.
nfsstat -s	writes > 5%	Install a Prestoserve NFS accelerator (SBus card or NVRAM-NVSIMM) for peak performance. See Section 4.6, "Prestoserve NFS Accelerator."

Table 5-1 (Continued)

Command/Tool	If the Command Output Is	Then
nfsstat -s	There are any badcalls.	The network may be overloaded. Identify an overloaded network using network interface statistics.
nfsstat -s	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 Section 4.7.6, "Directory Name Lookup Cache (DNLC)" in Chapter 4, "Configuration Recommendations for NFS Performance."
vmstat -s	hit rate (cache hits) < 90%	Increase ncsize in the /etc/system file.
Ethernet monitor, for example: SunNet Manager, SharpShooter (AIM Technology), NetMetrix (Hewlett-Packard)	load > 35%	Add Ethernet interface and distribute client load.

Table 5-2, Table 5-3, and Table 5-4 show potential bottlenecks by type and their solutions.

Table 5-2

Symptom(s)	Command/Tool	Cause	Solution
NFS server hostname not responding or slow response to commands or when using NFS-mounted directories.	nfsstat	User's path variable	List directories on local file systems first, critical directories on remote file systems second, and then the rest of the remote file systems.
NFS server hostname not responding or slow response to commands or when using NFS-mounted directories.	nfsstat	Running executable from an NFS mounted file system	Copy the application locally (if used often).
NFS server hostname not responding; badxid >5% of total calls and badxid = timeout.	nfsstat -rc	Client times out before server responds	Check for server bottleneck. If server's response time isn't improved, increase the timeo parameter in the /etc/vfstab file of clients. Try increasing timeo to 25, 50, 100, 200 (tenths of seconds). Wait one day between modifications and check to see if number of time-outs is decreasing.
badxid = 0.	nfsstat -rc	Slow network	Increase rsize and wsize in the /etc/vfstab file. Check interconnection devices (bridges, routers, gateways).

Table 5-3

Symptom(s)	Command/Tool	Cause	Solution
NFS server hostname not responding.	vmstat -s or iostat	Cache hit rate is <90%.	Adjust the suggested parameters for DNLC, then run to see if the symptom disappears. If not, reset the parameters for DNLC. Adjust the parameters for the buffer cache, then the inode cache, following the same procedure as for the DNLC.
NFS server hostname not responding.	netstat -m or nfsstat	Server not keeping up with request arrival rate.	Check network. If the problem is not network, add appropriate Prestoserve NFS accelerator, or upgrade the server.
High I/O wait time or CPU idle time. Slow disk access times or NFS server hostname not responding.	iostat -x	I/O load not balanced across disks. The svc_t value is greater than 40 ms.	Take a large sample (~2 weeks). Balance the load across disks; add disks as necessary. Add a Prestoserve NFS accelerator for synchronous writes. To reduce disk and network traffic, use tmpfs for /tmp for both server and clients. Measure system cache efficiencies. Balance load across disks; add disks as necessary.
Slow response when accessing remote files.	netstat -s or snoop	Ethernet interface dropping packets.	If retransmissions are indicated, increase buffer size. For information on how to use snoop, see Section A.2.1, "Snoop."

Table 5-4

Symptoms	Command/Tool	Cause	Solution
Poor response time when accessing directories mounted on different subnets or NFS server hostname not responding.	netstat -rs	NFS requests being routed	Keep clients on subnet directly connected to server.
Poor response time when accessing directories mounted on different subnets or NFS server hostname not responding.	nfsstat	Dropped packets	Make protocol queues deeper.
Poor response time when accessing directories mounted on different subnets or NFS server hostname not responding.	netstat -s shows incomplete or bad headers, bad data length fields, bad checksums.	Network problems	Check network hardware.
Poor response time when accessing directories mounted on different subnets or NFS server hostname not responding. The sum of input and output packets per second for an interface is over 600 per second.	netstat -i	Network overloaded	The network segment is very busy. If this is a recurring problem, consider adding another (le) network interface.
Network interface collisions are over 120 per second.	netstat -i	Network overloaded	Reduce the number of machines on the network or check network hardware.
Poor response time when accessing directories mounted on different subnets or NFS server hostname not responding.	netstat -i	High packet collision rate (Collis/Opkts >.10)	If corrupted packets, may be due to corrupted MUX box; use Network General Sniffer or another protocol analyzer to find cause. Check for overloaded network. If there are too many nodes, create another subnet. Check network hardware; could be bad tap, transceiver, hub on 10base-T. Check cable length and termination.