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NetWare Internal and External Bridge
Performance Benchmarking
Drew F. Jackman
Associate Consultant
Systems Engineering Division
Abstract:
One of the key factors of network optimization is performance. Bridges are
used on the local area networks to increase the performance of a particular
section within the network. In doing this, the traffic between sections
(over the bridge) suffers. A network administrator must decide which
bridging configuration will give the best performance: internal or
external, dedicated or nondedicated. When integrating a bridging
configuration, all costs must be weighed against the advantages and
disadvantages.
Introduction
This document describes two network bridging configurations for NetWare
LANs (internal and external) and summarizes the benchmarking tests
performed on these configurations. The benchmarking tests were designed to
isolate the bridging machine as the device under test, with all other
network elements kept constant. This method shows any change to the
bridging machine reflected in the results of the performance tests (in the
throughput). One test was conducted as a control, and is the standard to
which all the other tests will be compared.
Throughout this document the terms bridge and router are interchangeable,
since the NetWare products operate at the network layer (third) of the Open
Systems Interconnection (OSI) model instead of at the data-link layer
(second). But in keeping with terminology originally used by Novell for
this particular function, the term bridge is used.
All 286 NetWare bridges can connect up to four subnets to make an
internetwork appear as one logical network. Each bridge in a network keeps
a dynamic routing table containing the addresses of the other nodes on the
network. It contains the fastest route to each node, and for better
reliability, it also contains a list of alternate routes that can be used
if the primary route were to go down.
Interesting points illustrated by this testing are: (1) the comparison
between internal and external bridges, (2) the comparison between SFT
NetWare v2.15 and NetWare 386 v3.0, (3) the degradation curve caused by
adding external bridges in series, and (4) the performance comparison
between a dedicated and a nondedicated bridge.
Bridges
NetWare bridges are internal and external. An internal bridge is contained
within a file server and operates along with the normal file server
functions. Thus an internal bridge is actually bridging information through
a file server to another network or backbone on the LAN. An external bridge
is a separate machine running the bridging software that connects multiple
networks. This type of bridge can function in one of two ways: solely as a
bridge (dedicated), or as a bridge that simultaneously functions as a
workstation (nondedicated). A bridge functions as the buffer between two
similar or dissimilar protocols. It can also be used to break one large
network into two smaller ones to increase the performance of each by
reducing the traffic on the wire.
An external bridge used strictly as a bridge is called a dedicated bridge.
A dedicated bridge does nothing but interconnect multiple networks by
conveying data among them.
An external bridge that functions as a bridge and as a workstation
simultaneously is called a nondedicated bridge. In a nondedicated bridge
the bridging software runs on top of DOS and the workstation shell. In
addition to the possible degradation in processing speed of the workstation
and bridge (due to both processes occurring simultaneously on the same
machine), there is also a possibility that the other applications running
on that workstation will malfunction and cause the bridging process to
stop. All the workstations connected through the bridge/workstation will be
cut off from the network on the opposite side of the bridge.
Test description
Each of the tests was configured and performed with the purpose of
isolating the bridging section as the test module.
Hardware
The benchmark tests were performed with the following hardware
configurations. Each of the tests was performed by accessing a Novell 286B
file server set at 8MHz with 0 wait states. This file server was installed
with a Novell Disk Coprocessor Board (DCB), a CDC WREN III embedded SCSI
drive, and an NE2000 Ethernet adapter. The file server was accessed through
the different bridging devices (see Figure XX).
The dedicated and nondedicated internal 2.15 and 3.0 file server tests were
performed using a Compaq 386 25MHz computer, installed with an ISADISK disk
driver and 2MB of memory (the minimum amount needed to run NetWare 386).
The nondedicated file servers were kept busy with a single Novell 286A
workstation logged in and running the performance evaluation test program
(PERFORM2 described below). The two internal configurations were run a
second time using a 286B 8MHz computer installed with a Novell DCB. This
enabled a comparison of the internal and external bridges. Each of the
internal bridge tests used five Samsung 386S 20MHz computers and one Novell
386AE 16MHz computer as the workstations (see Appendix A).
All internal bridge tests were performed using NE2000 Ethernet adapters in
the file server, the bridging machine and the workstations. Thin cable
Ethernet (RG-58 A/U) was used to connect the network.
Figure 1: General block diagram of the bridging test setup
The external bridge tests used the same six workstations used in the
internal bridge tests. The computers used as the dedicated external bridges
were 8MHz 286As, set at 0 wait states. The nondedicated bridge tests also
used one (or two) of the same 286As as the bridging devices. All of the
external configurations were connected by NE2000 Ethernet adapters. The
only exception occurred during the multiple dedicated bridge tests where
NE1000 Ethernet adapters were used in the workstations, with NE2000s in the
bridges and the file server.
During the read overlaid performance test (described below) the workstation
adapter had little or no effect on the degradation of the final throughput
because all six workstations were transmitting through one conduit-the
bridge adapter and file server adapter. The workstation adapters wait for a
turn to transmit through the bridge and file server adapters. Thus the
NE1000s used in the workstations during the external dedicated tests had no
effect on the final system throughput when compared with the NE2000s used
in the workstations. To isolate the bridging device as the test module, the
file server adapter and bridging adapter were not changed, but the bridging
configuration was changed. Thus each test examined the bridging device
only.
Software
The operating system on the file server of Figure XX was SFT NetWare v2.15.
The bridging file servers (internal bridges) were booted with either SFT
NetWare v2.15 or NetWare 386 v3.0. The external bridges were booted from
the bridging software included in the NetWare 2.15 software package. The
dedicated bridges were configured in real mode and the nondedicated in
protected mode (see SFT/Advanced Bridges manual for more information). The
tests were executed using the PERFORM2 (version 2.3) performance evaluation
program,which has a record size of 4,096 bytes and 1,000 iterations for
each test.
Only the read overlaid function of PERFORM2 was used during the
benchmarking tests, which enabled testing of only the bridging component.
Workstations making overlaid read requests access the same data repeatedly.
After the first workstation accesses the information from the hard disk, it
is in the file server's cache memory to be used by all the workstations
requesting it, eliminating the hard disk access speed from the test. Since
all test configurations access the data from memory at the same speed, the
file server memory access is also eliminated from the tests. This leaves
only the degradation caused by the bridging device-the intended result of
the tests. The NetWare 386 v3.0 internal bridge tests were run several
times to allow the dynamic memory allocation to stabilize (see Technical
Overview; NetWare 386, ppg. 21 and 22).
Configuration
The internal bridge configurations tested were as follows:
Dedicated bridging v2.15 file server
Nondedicated bridging v2.15 file server (nondedicated, in this case,
meaning that it is busy performing its file server functions while it is
bridging)
Dedicated 386 v3.0 file server
Nondedicated 386 v3.0 file server (nondedicated meaning that it is busy
being a file server)
The external bridge configurations tested included the following:
Dedicated bridge configurations with from one to six bridging machines in
series
Nondedicated bridge
Two nondedicated bridges in series
Test Results
The first configuration tested was the control model with no bridging. The
resulting throughput was 623 Kbyte/s. This value was used to compare the
degradation experienced by the other bridging configurations.
Internal
The results of the internal bridge tests demonstrate the immediate
performance degradation caused by bridging. As displayed in Figure XX, a
substantial performance drop occurs when network packets or requests pass
through a bridging device. For this configuration, the drop is a 41 percent
decrease in throughput. This is the best possible throughput for this
configuration.
The next point illustrated by the internal bridge tests is the performance
comparison between the two versions of NetWare (SFT v2.15 and 386 v3.0). As
shown in Figure XX both types of file servers functioned at approximately
the same level of throughput.
Figure 2: Internal bridge comparison
External
A NetWare external bridge can be configured as dedicated or nondedicated.
The first test performed on the external bridges involved adding from one
to six dedicated bridges in series and testing the throughput of the system
as each bridge was added (see Appendix A). The results of this test show
the resulting performance degradation curve (see Figure XX). This happens
when information passes through an internet with multiple bridges between
the accessing workstation and the intended file server. A similar
performance curve would occur when information passes through multiple
internal bridges.
Figure 3: Multiple bridge degradation curve
The initial degradation through the first bridge results in a 43 percent
drop in throughput. Each additional bridge adds a small percentage to this
initial performance degradation. Table I contains each percentage, from one
to six bridges, as compared to the configuration with no bridge (no bridge
is equal to a zero percent drop in throughput). For example, for six
bridges in series, there is an 81 percent throughput degradation compared
to the no bridge test. This makes the throughput of a six bridge network
only 19 percent of a no bridge network's throughput. If more bridges were
added, the curve in Figure XX would continue in a steady decline. After a
total of sixteen bridges, NetWare would eliminate the packet to ensure that
the packet would not continue through a circular internet connection.
Table I: Percent performance degradation compared to no bridge
Number of bridges 1 2 3 4 5 6
Performance drop 43% 52% 60% 72% 76% 81%
The nondedicated bridge tests were run by operating the performance
evaluation test (PERFORM2) in two network drives (see Figure XX). One
directory had six workstations simultaneously performing the test, while
the bridges/workstations were in another directory running the same type of
test. The workstations were physically connected through the bridge(s).
Figure 4: Nondedicated bridge hardware and software setup
The results show that the nondedicated bridge is the slowest of the
bridging configurations. With one nondedicated bridge the throughput drops
60 percent. With two nondedicated bridges in series the performance drop is
67 percent. Figure XX illustrates the performance of the nondedicated
configuration as compared to the test using no bridge. These results
represent the throughput for the six workstations, not the throughput of
the bridge/workstations. During the nondedicated test, the
bridge/workstations were cut to less than 10 percent of the throughput
shown in the test using no bridge. The workstation installed with the
bridging software was slowed down to approximately
30 to 60 Kbyte/s.
Figure 5: Nondedicated bridge degradation
A performance comparison between the two types of external bridges is shown
in Figure XX. Because the nondedicated bridges are functioning
simultaneously as workstations, throughput is slowed. A user can expect an
average of 30 percent less performance (throughput) through a nondedicated
bridge.
Figure 6: Comparison of dedicated and nondedicated bridge performance
The next comparison that can be drawn from the bridging tests is between
internal and external bridges (dedicated and nondedicated). The results of
the internal and external bridge comparison show the internal bridge has a
10 percent slower throughput. If the nondedicated configurations are
compared, the internal bridge has a 15 percent slower throughput (see
Figure XX). If the internal bridge is heavily loaded with file server
tasks, its throughput is even slower. Remember this set of internal bridge
tests used a 286B file server so the comparison between internal and
external would be valid.
Figure 7: Comparison of internal and external bridges
These results indicate the nondedicated internal bridge configuration is
the slowest type of bridge when a file server with a slow processor is used
(clock and processor). By picking a fast file server carefully, this
problem can be eliminated. If the bridging file server is heavily loaded
down, the throughput will decline whether the file server is fast or not.
Conclusion
The information contained in the test results shows some important points
that need to be emphasized. The first is the unavoidable performance
degradation (throughput degradation) that occurs when information passes
through a bridging device. The second is the comparison between external
and internal bridges. The third is throughput comparison between the two
versions of NetWare (286 v2.15 and 386 v3.0), and the fourth and final
point is the curve obtained as information passes through multiple bridges.
When a bridge is placed on an internet, the best possible throughput for
the information passing through the bridge is approximately 60 percent, as
compared to the throughput of an internet without the bridge. If multiple
bridges are added, or the bridging machine has a slow clock speed and
processor, the throughput will be reduced even more.
Figure 8: Comparison of performance drop corresponding to each type of
bridge
There are two things to consider when deciding between an internal and an
external bridge. The first is the overall cost of adding the new software
and hardware. The second is the performance (throughput) achieved with the
chosen bridge type. For example, if there are multiple file servers on one
backbone, and some of the workstations on that backbone need to access a
second backbone, one option is using an internal bridge. The only
additional cost is the installation of an extra adapter in one of the
existing file servers, to make it the internal bridge between the two
backbones. The performance would depend on how busy the new bridging file
server is, and how fast the file server hardware operates (clock and
processor speed). The throughput, compared to no bridge, would be from 40
percent to 60 percent. This would be a reliable bridging configuration (see
Table II). The best solution in this case is a fast file server that is not
heavily used. If a dedicated external bridge is chosen, the average
performance would be better than with an internal bridge, but the cost is
greater. The throughput would stay around 60 percent. A new machine with
two new adapters is needed as the bridge. This would be the best choice if
performance maximization and reliability are the ultimate goal.
The final possible configuration in this situation is using an existing
workstation as a nondedicated external bridge. The only expense is the
extra adapter. This configuration is inexpensive, but would also result in
a very slow throughput. It could also cause malfunctions between the two
backbones periodically. The system throughput would average around 40
percent of the configuration using no bridge, and the bridge/workstation
throughput would be less than 10 percent.
Table II: Advantages and disadvantages of bridging configurations compared
Option Reliability Performance Additional Restrictions
No bridge High 100% None Cannot split traffic
Internal Medium 40-60% One extra Bridging server can
be tied up
Dedicated Medium 60% Extra machine None
external and two adapters
Non- Low 30-40% One extra Applications on the
dedicated adapter BR/WS can hang.
Performance across
the BR/WS about 10
percent.
The reliability factor is a gauge of whether the bridge is likely to go
down.
Another question to address when creating an internal bridge is which
operating system will give the best throughput, 286 v2.15 or 386 v3.0. The
answer is simple-both operate the bridging function equally well. Use
whichever is most convenient. Whether they will perform equally when both
file servers are heavily loaded remains to be seen in a future test.
With a large internet information may pass through more than one bridge. As
shown in Table II, the initial drop through the first bridge is about 40
percent (making the throughput 60 percent as compared with no bridge). Each
additional bridge drops the resulting throughput an average of eight
percent. If throughput from one backbone to another is vital, then a one
(or a no) bridge maximum should be designed into the internet. The criteria
for deciding which configuration of bridges to use in an internet follows:
No bridge: high throughput unless there is high traffic, no extra cost
External dedicated bridge: consistently high throughput, high setup cost
External nondedicated bridge: low throughput, medium to low setup cost
Internal bridge: medium to high throughput, low setup cost
Appendix A
Figure 9: Test setup for dedicated internal bridges
Figure 10: Test setup for nondedicated internal bridges
Figure 11: Test setup for multiple external bridges
Appendix B
Table III: Data gathered from the benchmarking tests
Configuration Throughput Utilization Utilization
Kbyte/s bridging accessed
file server file server
No bridge between the
file server and
workstations 622.92 N/A 98%
Internal bridge in
a NetWare v2.15 363.57 69% 97%
dedicated file server
using 386 processor
Internal bridge in
a NetWare v2.15 366.88 87% 97%
nondedicated file server
using 386 processor
Internal bridge in
a NetWare v3.0 365.20 68% 97%
dedicated file server
Internal bridge in
a NetWare v3.0 364.26 85% 95%
nondedicated file server
Internal bridge in
a NetWare v2.15 320.61 100% 85%
dedicated file server
using 286 processor
Internal bridge in
a NetWare v2.15 213.37 99% 56%
nondedicated file server
using 286 processor
External dedicated
bridge 365.39 N/A 93%
Two external dedicated
bridges 295.97 N/A 78%
Three external
dedicated bridges 251.86 N/A 67%
Four external
dedicated bridges 172.52 N/A 45%
Five external dedicated
bridges 150.83 N/A 40%
Six external dedicated
bridges 119.50 N/A 30%
External nondedicted
bridge 250.31 N/A 65%
Two external
nondedicated bridges 206.72 N/A 57%