HP StorageWorks 2/24 FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN Env - Page 170

Implementing SAN Internetworking Solutions 4 • Rate limiting - If ingress traffic enters the SAN router faster than egress traffic leaves, port buffers fill and cause dropped data packets. Dropped packets cause TCP to resort to internal (and inefficient) flow control, causing dramatic link throughput decrease. Rate limiting prevents this problem. Refer to Intelligent Port Speed for detailed information about rate limiting. • Data compression - SAN router software identifies repetitive information in an output data stream and applies a compression algorithm to ensure the data is more compact and efficiently transmitted. The compression algorithm is set at the Element Manager application using the Compression Method drop-down list at the Advanced TCP Configuration dialog box. The list provides four algorithm selections: - LZO - The Lempel-Ziv-Oberhumer (LZO) compression algorithm searches for strings of characters duplicated within a block of data being compressed. Duplicated strings are removed from the data stream and replaced by an encoded string. Non-duplicate characters (literals) are output with special encoding to distinguish them from duplicate string encoding. LZO generates a self-contained compressed data block. All information needed to decompress the data is in the compressed data, and there is no history maintained by sender (for compression) or the receiver (for decompression). The algorithm is recommended when up to 64 TCP sessions are used and the available bandwidth is up to 155 Mbps (OC-3 transport level). - Fast LZO with history - This algorithm uses the LZO algorithm with a history cache. A history cache is maintained and used to more effectively compress and decompress data. The algorithm has an average compression ratio increase of approximately 20% over LZO. The algorithm is recommended when up to 8 TCP sessions are used and the available bandwidth is up to 155 Mbps (OC-3 transport level). - LZO with history - This algorithm incorporates the LZO algorithm with a history cache and Huffman encoding. Huffman encoding is an algorithm for lossless compression based on the statistical frequency of occurrence of a symbol in the file being compressed. As the probability of occurrence of a symbol increases, the compressed bit-size representation decreases. The algorithm uses additional computing resources 4-26 McDATA Products in a SAN Environment - Planning Manual