System information

4
Configuring iSAN Connections
4-11
Configuring TCP Ports for iFCP
• HW - All transmitted data is compressed using the hardware
feature in the SAN router. This is the recommended setting if
the remote destination also supports HW compression.
• SW - All transmitted data is compressed, using the SAN
router’s CPU. Use this setting when you need to use as little
bandwidth as possible and the remote destination does not
support hardware compression. Note that effective
throughput with the “SW” setting may be less than the
effective throughput seen with the “SW as needed” setting,
especially at link speeds greater than T3.
• SW as needed - Depending on the available bandwidth,
decision are dynamically made whether or not to compress
transmitted data. With SW As Needed setting on, the port keeps
the egress data rate as close as possible to the port speed of the
port.
2. Specify the compression algorithm by selecting the Compression
Method. Compression is an optional software feature; the
Compression Method field is enabled only if the Compression Level is
SW or SW as needed.
The multiple compression methods allow a trade-off between
compression rate (speed) and compression ratio (amount of
compression). The following options are available for Compression
Method:
• LZO - performs compression on a frame-by-frame basis. This
method is best when there are many active initiator-target
sessions. This is the default setting.
• Fast LZO with History - performs compression two bytes at a
time with eight kB of history. This works best with fewer
active iFCP initiator-target sessions and a fast remote link.
• LZO with History - performs compression one byte at a time
with eight KB of history. LZO w/History gives the next best
compression ratio, but has a compression rate of about 25
MB/s. For link Rates of 100 Mb/s or less use LZO w/History.
This works best with fewer active iFCP initiator-target
sessions and a medium speed remote link (for example, T3).
• Deflate - provides the best compression ratio, but has the
lowest compression rate. For link rates of 10 Mb/s or less use
Deflate (may be called ZLIB). This is best for slow links, such at
T1, with any number of active iFCP initiator-target sessions.