Author: Tom
Robinson
I-TECH Corp.
If developers
and manufacturers of products for storage infrastructure are
considered to be on the leading edge of new storage technologies,
test equipment vendors can be considered to be on the “leading
edge of the leading edge.” And the latest leading edge
is a significant shift from parallel to serial technologies.
The evolution
of parallel SCSI interface test equipment was relatively straightforward
through the introduction of Ultra320 SCSI in which electrical
performance limitations resulted in cross-talk, low-level
ground noise, and signal skew. This new generation of SCSI,
Serial Attached SCSI (SAS), specifies the established SCSI
protocol as a new gigabit serial technology.
SAS tester
and analyzer development is a natural transition for test
vendors who have provided test equipment for both parallel
SCSI and serial gigabit technologies. They can easily leverage
past experience with these technologies into a new generation
of testers and protocol analyzers.
SAS testers
act as a controlled, often programmable, initiator or target
for generating I/Os to or through a storage device. Low-level
control allows a user to test a device for its response or
recovery to expected or unexpected data conditions. Protocol
analyzers, on the other hand, unobtrusively buffer data into
on-board memory from a device port or multiple ports on a
network. Hardware logic and application software enable users
to view the captured data and apply tools for fault isolation,
protocol compliance and performance monitoring.
One significant
difference between parallel and serial test equipment is in
the analyzer software application. A parallel SCSI analyzer
generally provides trace view formats for the many lines of
parallel data that make up a progressive thread of I/Os (or
phases). Since only one device may communicate with one other
device at a time, the feature set is limited, in contrast
to a serial analyzer.
A serial
analyzer typically provides a multi-channel interface supporting
the correlation of multiple test points (communication links)
in a single view and features for simultaneous operation of
multiple channels. For example, a SAS trigger strategy may
be configured to monitor several conditions across several
links.
Because
serial technologies, such as SAS, have framed transport architectures,
test equipment needs to address this. Serial testers support
the creation and user-defined editing of serial frame architecture,
primitives, and payload. Analyzers time correlate and decode
the data they capture into a trace view, supported by numerous
features to navigate through the trace data. The trace views
display the full frame architecture, primitives, and payload
in user-defined formats, depending on the application.
To accommodate
the increase in serial interface options available to the
storage market, test vendors will be working toward consolidating
support for multiple protocols into common, cost-effective
platforms. Already, test solutions are available that combine
time-correlated options for Fibre Channel, SATA, SAS, and
Gigabit Ethernet serial technologies in common system platforms.
This is a critical path as, in most cases, developers are
designing products for more than one serial interface and
require test solutions that provide a cost-effective and shared
resource platform.
