User's Guide

If you w
ere planning for a maximum of 50 concurrent swagent processes, you might begin to run
into problems since the system is likely to start to swap (800Mb of real memory and 1200Mb of
virtual memory would be required).
Do not add real and virtual memory together when trying to determine if you need more swap or
physical memory in a system; the amount of virtual memory consumed by swagent includes the
real memory used.
When a lot of memory has been consumed by swagent processes, the buffer cache would be
significantly reduced. This leads to performance bottlenecks due to accessing SD depots on disk. A
large buffer cache (assuming that multiple swagent processes are accessing the same depot) will
increase the likelihood that swagent processes will read data from the buffer cache rather than
directly from disk. How large that buffer cache should be is beyond the scope of this discussion.
If you need to have a lot of concurrent SD sessions running on the Ignite server, carefully consider
the trade-off between cost and performance. Large JBODs will hold a lot of SD depots, but the
speed of your installs will be limited if you have a very small buffer cache and the data must be
read from disk constantly by multiple swagent processes. If you have a JBOD that has a lot of
read requests from swagent processes reading depots, you might consider relocating the data to
a higher performance device such as an HP XP or EVA disk array, or you could add more physical
memory to your system to allow it to be used as buffer cache.
Network Bandwidth
The following section is based on assumptions that may or may not be true in your environment.
The main purpose of this section is to help you understand how multiple SD sessions using one LAN
interface can affect how long it takes to install a system via the network.
The following is a comparison of 100BT and Gigabit Ethernet network interfaces. The examples
assume throughput rates on the LAN interfaces, and that a number of systems would all start an
install at the same time using the same SD depot.
If you have an 100BT interface, and assuming that SD gets about 60 megabits per second, 60
systems pulling a 3Gb depot SD gives you the following amount of time to install a system:
60*3*1024 / ((60/8)*3600) = 184320 / 27000 = 6.82 hrs to complete
If you can achieve 300 megabits through a Gigabit Ethernet interface, that dramatically drops the
time required (assuming that the system is fast enough to push that much data from SD through):
60*3*1024 / ((300/8)*3600) = 184320 / 27000 = 1.36 hrs to complete
The calculation is:
Number of concurrent systems * depot size (in Mb, hence 3*1024)
That is divided by:
Lan speed (in megabits)/8 (to get Megabytes per second) * 3600
194