HP StorageWorks Enterprise File Services WAN Accelerator Deployment Guide (November 2005)

14 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 a
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 out 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.