18Administering Extended Fabrics; Extended Fabrics Licensing; Extended Fibre Channel Over Distance; Distance Levels For Extended Inter-Switch Links (Isls) - HP A7533A - Brocade 4Gb SAN Switch Base Administrator's Manual

Hp storageworks fabric os 6.x administrator guide (5697-0015, may 2009)
Hide thumbs Also See for A7533A - Brocade 4Gb SAN Switch Base:
Table of Contents

Advertisement

18
Administering Extended Fabrics
This chapter provides information on implementing Extended Fabrics software.

Extended Fabrics licensing

To implement long distance dynamic (LD) and long distance static (LS) distance levels, you must first install
the
Extended Fabrics license
switches used on both ends of the extended ISL.

Extended Fibre Channel over distance

Extended Fabrics software optimizes switch buffering to ensure the highest possible performance on inter-
switch links (ISLs). When Extended Fabrics is installed on gateway switches, the ISLs (E_Ports) are
configured with a large pool of buffer credits. The enhanced switch buffers help ensure that data transfer
can occur at near-full bandwidth to efficiently utilize the connection over the extended links.
The Extended Fabrics feature extends the distance the ISLs can reach over a dark fiber or wave division
multiplexing (WDM) connection. This is accomplished by providing enough buffer credits on each side of
the link to compensate for latency introduced by the extended distance.

Distance levels for extended Inter-Switch Links (ISLs)

As the distance between switches and the link speed increases, additional buffer credits are required for
the ports used for long distance connections. Distance levels define how these buffer credits are allocated
and managed for extended ISLs. Buffer credits are managed from a common pool available to a group of
ports on a switch. The buffer credit, can be changed for specific applications or operating environments,
but must be in agreement among all switches to allow formation of the fabric.
Information about switch characteristics and capacity in terms of buffers per port group, port speed, and
distances supported is in
distance level, and for estimating the impact an extended ISL may have on buffer availability and port
performance.

Buffer-to-Buffer Credits

Buffer-to-buffer (BB) credit flow control is implemented to limit the amount of data a port may send based
on the number and size of the frames sent from that port. Buffer credits represent finite physical port
memory. Within a fabric, each port may have a different number of BB credits. Within a connection, each
side may have a different number of BB credits. One buffer credit allows a device to send one payload up
to 21 12 bytes (2148 with headers). Assuming that each payload is 21 12, you need one credit per 1 km of
link length at 2 Gbps (smaller payloads require additional BB credits to maintain link utilization).
The final frame size must be a multiple of 4 bytes. If the data (payload) needs to segment, it will be padded
with 1 to 3 "fill-bytes" to achieve an overall 4 byte frame alignment. The standard frame header size is 24
bytes. If applications require extensive control information, up to 64 additional bytes (for a total of an 88
byte header) can be included. Because the total frame size cannot exceed the maximum of 2,148 bytes, the
additional header bytes will subtract from the data segment size by as much as 64 bytes (per frame). This
is why the maximum data (payload) size is 2,1 12 (because [2,1 12 – 64] = 2,048, which is exactly 2K-bytes
of data). The final frame, after it is constructed, is passed through the 8 byte to 10 byte conversion process.
. Use the licenseShow command to verify that the license is present on both
Table 81
on page 368. This table may be useful in choosing an appropriate
Fabric OS 6.x administrator guide 363

Advertisement

Table of Contents
loading

This manual is also suitable for:

Ae370a - brocade 4gb san switch 4/12

Table of Contents