HP StorageWorks Enterprise File Services WAN Accelerator 3.0.4 deployment guide (AG421-96001, March 2007)

16 1 - DESIGNING AN HP EFS WAN ACCELERATOR DEPLOYMENT
Transaction
Acceleration
Transaction Acceleration (TA) is composed of the following optimization
mechanisms:
 A connection bandwidth-reducing mechanism called Scalable Data Referencing
(SDR).
 A Virtual TCP Window Expansion (VWE) mechanism that repacks TCP
payloads with references that represent arbitrary amounts of data.
 A latency reduction and avoidance mechanism called Transaction Prediction
(TP).
SDR and TP can work independently or in conjunction with one another depending on
the characteristics and workload of the data sent across the network. The results of the
optimization vary, but typically result in throughput improvements in the range of 10
to 100 times over unaccelerated links.
Scalable Data
Referencing
Bandwidth optimization is delivered through Scalable Data Referencing (SDR). SDR
uses a proprietary algorithm to break up Transmission Control Protocol (TCP) data
streams into data chunks that are stored in the hard disk (data store) of the HP EFS
WAN Accelerator. Each data chunk is assigned a unique integer label (reference)
before it is sent to the peer HP EFS WAN Accelerator across the WAN. If the same
byte sequence is seen again in the TCP data stream, then the reference is sent across
the WAN instead of the raw data chunk. The peer HP EFS WAN Accelerator uses this
reference to reconstruct the original data chunk and the TCP data stream. Data and
references are maintained in persistent storage in the data store within each HP EFS
WAN Accelerator. There are no consistency issues even in the presence of replicated
data.
How Does SDR
Work?
When data is sent for the first time across a network (no commonality with any file
ever sent before), all data and references are new and are sent to the HP EFS WAN
Accelerator on the far side of the network. This new data and the accompanying
references are compressed using conventional algorithms, when and if it improves
performance.
When data is changed, new data and references are created. Thereafter, whenever new
requests are sent across the network, the references created are compared with those
that already exist in the local data store. Any data that the HP EFS WAN Accelerator
determines already exists on the far side of the network are not sent—only the
references are sent across the network.
As files are copied, edited, renamed, and otherwise changed or moved, the HP EFS
WAN Accelerator continually builds the data store to include more and more data and
references. References can be shared by different files and by files in different
applications if the underlying bits are common to both.
Virtual Window
Expansion
Virtual TCP Window Expansion (VWE) allows HP EFS WAN Accelerators to repack
TCP payloads with references that represent arbitrary amounts of data. This is possible
because unlike other compression products, HP EFS WAN Accelerators operate at the
application layer and terminate TCP, which gives them more flexibility in the way they
optimize WAN traffic.