HP Storageworks 8100 - enterprise virtual array, User Manual

Page: 129 / 408

Encryption boxes on the WAN link often add a few bytes to each frame, so it may be necessary to
decrease the MTU size to 1450 to allow the encryption box add the bytes and keep the MTU size
under 1500 bytes.
NOTE:
Jumbo frames are not supported for use with HP Continuous Access EVA Continuous Access.
Compression
The MPX200 integrates a software compression option. Enable compression for IP fabrics with an
RTT greater than or equal to 40 ms; or guaranteed WAN bandwidth of less than or equal to 200
Mb/s. See “
TCP window size recommendations ” on page 130 for compression options for specific
network rates and RTT.
TCP window size/scaling performance tuning
The MPX200 FCIP performance is maximized when properly configured. Knowing the RTT (distance)
between MPX200 Multifunction Routers and the WAN dedicated or guaranteed bandwidth allows
the gateways to be tuned for optimal performance. See
Modifying the window size and scaling factor .
Modifying the window size and scaling factor
The MPX200 window size can be set to a maximum of 32 KB. The scaling factor is used as a multiplier
to increase the window size above 32 KB. Modify the window size and scaling factor in the MPX200
Multifunction Router pairs based on the WAN RTT and link speed. To determine the appropriate
window size setting, use the pre-populated tables or a formula.
If the recommended TCP window size scale factor for a given RTT and WAN link speed is not shown
in
Table 17 through Table 23 , use the formula:
(RTT (ms) x link rate (Kb/s) x (1 byte/
8 bits) = minimum window size (MWS).
Then, convert the MWS to a recommended scale factor by dividing it by the default window size
(32,768 bytes). Use
Table 16 to determine the scale factor.
Table 16 TCP window size scale factors
Scale factor MVS scale result
0 0 to 2
1 2 to 4
2 4 to 8
3 8 to 16
4 16 to 32
5 32 to 64
6 64 to 128
7 128 to 256
MPX200 Multifunction Router 129