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and results in a lower compression bandwidth. The algorithm
has an average compression ratio increase of approximately
30% over LZO. The algorithm is recommended when up to 8
TCP sessions are used and the available bandwidth is between
10 Mbps (thin Ethernet) and 45 Mbps (DS3 transport level).
— Deflate - This algorithm incorporates a history cache with
Huffman encoding. In addition, a hash table (saved in the
compressed data) is used to perform string searches. Deflate is
a processor-intensive algorithm with the highest compression
ratio. The algorithm is restricted to use for 10 Mbps (thin
Ethernet) links.
Note that a data compression ratio cannot be definitively stated,
because it changes instantaneously with every data byte
transmitted. A consistent byte pattern can be compressed more
than a random byte pattern. For example, a defined, constant
pattern can often be compressed 15:1. Already-compressed data
(such as many graphic formats and some tape formats) cannot be
compressed further (1:1). Most data streams are compressible
from between 2:1 and 15:1, depending on the density of consistent
patterns. The only way to accurately determine a compression
ratio is to compress the data and measure the result.
•
FastWrite technology - SCSI is a simplex protocol that sends a
portion of a write command, then waits for a response. Multiple
commands can coexist, resulting in an inefficient process on
high-latency links. FastWrite is an algorithm that reduces the
number of round trips required to complete a SCSI write
command to one round trip. The software improves performance
over WANs by mitigating the effects of latency and using the
entire link bandwidth (because all data is transmitted
simultaneously).
The FastWrite algorithm responds to initiator write commands
with local transfer ready (XFR_RDY) commands that cause the
initiator to transmit an entire data set, then buffers the output
data at the SAN router closest to the corresponding target device.
This eliminates multiple XFR_RDY command transmissions and
minimizes bursty data transfer over the WAN, thus reducing
round-trip delays that are characteristic of extended-distance
links.
Implementing SAN Internetworking Solutions
Implementing SAN Internetworking Solutions
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