Serial Attached Scsi Technology - HP DL165 - ProLiant - G6 Introduction Manual

20 percent serial encoding overhead. Therefore, a PCIe 1.0 x4 link—with four send and receive
pairs—has an effective bandwidth of 2 GB/s and a x8 link has an effective bandwidth of 4 GB/s.
This flexibility allows slower devices access to a single lane with a relatively small number of pins
while giving faster devices more lanes as required. For example, the latest Smart Array SAS
controllers have x4 and x8 PCIe I/O connectors.
The PCIe 2.0 specification (supported by the ProLiant DL160 G5 server) doubles the per-lane
signaling rate of PCIe 1.0 from 2.5 Gb/s to 5 Gb/s, resulting in a total bandwidth of approximately
1 GB/s per PCIe link (Figure 4).
Figure 4. PCIe data transfer rates
Lane 1 Send
Lane 1 Receive
Source
n
Lane Send
n
Lane Receive
PCIe 2.0 is completely backward compatible with PCIe 1.0. A PCIe 2.0 device can be used in a PCIe
1.0 slot and a PCIe 1.0 device can be used in a PCIe 2.0 slot. Table 3 shows the level of
interoperability between PCIe cards and PCIe slots.
Table 3. PCIe device interoperability
PCIe x4 Connector
device type x4 Link
x4 card x4 operation
x8 card Not allowed
x16 card Not allowed

Serial Attached SCSI technology

Serial attached SCSI (SAS) is a point-to-point architecture in which each device connects directly to a
SAS port rather than sharing a common bus like parallel SCSI devices. Point-to-point links increase
data throughput and improve the ability to locate and fix disk failures. More importantly, the SAS
architecture solves the parallel SCSI problems of clock skew and signal degradation at higher
signaling rates. 5
For additional information about PCI Express technology, see the technology brief titled "HP local I/O strategy
4
for ProLiant servers" available at
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00231623/c00231623.pdf.
5 For more information about SAS technology, refer to the HP technology brief titled
technology" available at
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00301688/c00301688.pdf.
4
Link
size PCIe 1.0
x1 250 MB/s
Target
x4 1 GB/s
x8 2 GB/s
x16 4 GB/s
x8 Connector x8 Connector
x4 Link x8 Link
x4 operation x4 operation
x4 operation x8 operation
Not allowed Not allowed
Max. bandwidth
(Send or receive)
PCIe 2.0 PCIe 1.0
500 MB/s 500 MB/s
2 GB/s 2 GB/s
4 GB/s 4 GB/s
8 GB/s 8 GB/s
x16 Connector
x8 Link
x4 operation
x8 operation
x8 operation
"Serial Attached SCSI
Total
(Send and receive)
PCIe 2.0
1 GB/s
4 GB/s
8 GB/s
16 GB/s
x16 Connector
x16 Link
x4 operation
x8 operation
x16 operation
7