SkyWriter is delivered with a standard I/O interface supporting Ethernet, an asynchronous4.5.2 POWER Channel(tm)
SCSI controller, and a VME bus interface. Data can be transferred between the host CPUs and
the VME bus at 10MB/sec, while Ethernet speeds of 8-9 Mbits/sec are supported. There is a
single asynchronous SCSI channel capable of peak data transfers of 1.5MB/sec. This SCSI
controller does not allow for SCSI disk striping.
When there's a need for more performance than the standard I/O interface can handle,
SkyWriter users can obtain the POWER Channel option. POWER Channel is a replacement
I/Ointerface board which offers the following benefits:
o Synchronous SCSI support
o Improved Ethernet Performance
o Improved VME Bandwidth
o Two SCSI channels per System
By supporting the synchronous rather than asynchronous SCSI interface, the bandwidth to the
SCSI devices has been increased to 4MB/sec with peak transfer rates of 2.4MB/sec. SkyWriter
systems all support disk striping as well, allowing the user to distribute files across multiple
disks on a track-by-track or cylinder-by-cylinder basis to take advantage of the throughput of
multiple simultaneous disk accesses. Using striping, effective disk throughput can be increased
by up to 1.5X (striping across the maximum of 2 SCSI disks simultaneously - IP12 disks can be
striped 4 across for 2X-3X speedup).
With two SCSI channels on the POWER Channel board, up to 7 SCSI devices can be attached
to a single system, enabling the addition of up to 9.6GB of low-cost high-performance SCSI
secondary storage. VME-based SCSI controllers are also supported to enable the addition of
even more SCSI devices, and the new "tall-boy" external rack may be connected to hold up to
50GB more of additional storage devices.
POWER Channel supports not only faster disk throughput but faster VME bus and Ethernet
throughput. Ethernet performance has been increased to 1.25MB/second, the absolute limit of
the Ethernet specification. The VME bandwidth has been pushed from 10MBAec on the
standard I/O board to 32MB/sec, enabling much improved throughput between the CPU and
add-on IP12 disk controllers, third party I/O boards for A-to-D or D-to-A device
communication, or add-on networking boards.
4.6 Secondary Storage
A variety of disk and tape technologies are available for SkyWriter supporting a wide range of
requirements for on- and off-line storage of databases and other pertinent data.