Friday, September 02, 2005

Overview of Network Performance

Overview of Network Performance

¡Ü Congested or Collision - resend

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

¡Ü 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

¡Ü Latency

Not important as much as disk

Must consider that remote system has resources including disk

¡Ü 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

¡Ü Slower remote server

The remote server is CPU bound

¡Ü 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

¢º 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

¢º 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

¢º collision percentage > 5% (one system)

=> Checking the network interface and cabling

¢º collision percentage > 5% (all system)

=> The network is congested

¢º 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

¢º % of retrans of calls > 5% : maybe network problem

=> Looking for network congestion

=> Looking for overloaded servers

=> Check ethernet interface

¢º high badxid, as well as timeout : remote server slow

=> Increase the time-out period

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

¢º % 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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