Overview of Network Performance

● Congested or Collision - resend

Network has the bankwidth, and so can only transmit a certain amount of data

● EtherNet

10Mbit/sec(14,400 packes/sec)

Size of 1 packet - 64 bytes (about 14,400 packets/sec)

Maximum packet size : 1518 bytes

Inter packet gab : 9.6 micro-second

30-40% utilization because of collision contention

● Latency

Not important as much as disk

Must consider that remote system has resources including disk

● NFS

UDP : Common protocol in use, being part of TCP/IP and allows fast network throughput with little overhead.

Logical packet size : 9Kbytes

On ethernet : 6 * 1518 bytes

After collision, have to resend ALL serveral ethernet packets

● Slower remote server

The remote server is CPU bound

● Network Monitoring Tool

nfsstat

netstat

snoop

ping

spray

ping command

How to use ping

#> ping

Send a packet to a host on the network.

-s : send one packet per second

How to read ping -s output

▶ 2 single SPARCstations on a quiet EtherNet always respond with less than 1 millisecond

Example of ping

#> ping -s host
PING host: 56 data bytes
64 bytes from host (1.1.1.1): icmp_seq=0. time7. ms
64 bytes from host (1.1.1.1): icmp_seq=0. time7. ms


----host PING Statistics----
5 packets transmitted, 5 packets received, 0% packet loss
round-trip (ms) min/avg/max = 1/2/7
 

spray command

How to use spray

#> spray

Send a one-way stream of packets to a host

Reports How may were received and the transfer RATE.

-c : count(number) of packets

-d : specifies the delay, in microseconds

     Default: 9.6 microsecond

-l : specifies the Length(size) of the packet

How to read spray output

▶ If you use -d option, if there are many packet dropped the packet,

=> Check Hardware such as loose cables or missing termination

=> Check the possible a congested network

=> Use the netstat command to get more information

Example of spray

#> spray -d 20 -c 100 -l 2048 host

sending 100 packets of length 2048 to host ...
        no packets dropped by host
        560 packets/sec, 1147576 bytes/sec

netstat -i command

How to use netstat -i

#> netstat -i 5

errs : the number of errors

packets : the number of packets

colls : the number of collisions

* Collision percentage rate = colls/output packets * 100

How to read netstat data

▶ collision percentage > 5% (one system)

=> Checking the network interface and cabling

▶ collision percentage > 5% (all system)

=> The network is congested

▶ errs field has data

=> Suspect BAD hardware generating illegal sized packets

=> Check Repeated Network

Example of netstat

#> netstat -i 5
    input   le0      output         input  (Total)   output
packets errs packets errs colls packets errs packets errs colls
71853   1    27270   8    4839  72526   1    27943   8    4839
7       0    0       0    0     7       0    0       0    0   
14      0    0       0    0     14      0    0       0    0   

snoop command

How to use snoop

#> snoop

Capture packets from the network

Display their contents

Example of snoop

#> snoop host1
#> snoop -o filename host1 host2
#> snoop -i filename -t r | more
#> snoop -i filename -p99,108
#> snoop -i filename -v -p101
#> snoop -i filename rpc nfs and host1 and host2

nfsstat -c command

How to use nfsstat -c

#> nfsstat -c

Display a summary of servers and client statistics

Can be used to IDENTIFY NFS problems

retrans : Number of remote procedure calls(RPCs) that were retransmitted

badxids : Number of times that a duplicat acknowledgement was received for a single NFS request

timeout : Number of calls that timed out

readlink : Number of reads to symbolic links

How to read nfsstat data

▶ % of retrans of calls > 5% : maybe network problem

=> Looking for network congestion

=> Looking for overloaded servers

=> Check ethernet interface

▶ high badxid, as well as timeout : remote server slow

=> Increase the time-out period

   #> mount host:/home /home rw,soft,timeout=15 0 0

▶ % of readlink of the calls > 10% : too many symbolic links

Example of nfsstat

#> nfsstat -c

Client rpc:
calls   badcalls retrans badxid timeout wait newcred timers
13185   0        8       0      8       0    0       50

Client nfs:
calls   badcalls nclget  nclcreate
13147   0        13147   0
null    getattr  setattr root   lookup   readlink read
0  0%   794  6%  10   0% 0  0%  2141 16% 2720 21% 6283 48%
wrcache write    create  remove rename   link     symlink
0  0%   581  4%  33   0% 29  0% 4  0%    0  0%    0  0%
mkdir   rmdir    readdir statf
0  0%   0  0%    539  4% 13 0%

Network Solutions

1st. Consider adding the Prestoserve NFS Write accelerator.

=> Write % from nfsstat -s > 15%, consider installing it.

2nd. Subneting

=> If your network is congested, consider subnetting.

=> That is collision rate > 5%, subnetting.

3rd. Install the bridge

=> If your network is congested and physical segmentation is NOT possible.

=> Isolate physical segments of a busy network.

4st. Install the local disk into diskless machines.

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