HP DL165 Technologies for HP ProLiant 100-series G5 (Generation 5) servers, 2n - Page 7

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.4 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 Source Lane 1 Send Lane 1 Receive Target Lane n Send Lane n Receive Link size x1 x4 x8 x16 Max. bandwidth (Send or receive) PCIe 1.0 PCIe 2.0 250 MB/s 500 MB/s 1 GB/s 2 GB/s 2 GB/s 4 GB/s 4 GB/s 8 GB/s Total (Send and receive) PCIe 1.0 PCIe 2.0 500 MB/s 1 GB/s 2 GB/s 4 GB/s 4 GB/s 8 GB/s 8 GB/s 16 GB/s 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 device type x4 card x8 card x16 card x4 Connector x4 Link x4 operation Not allowed Not allowed x8 Connector x4 Link x4 operation x4 operation Not allowed x8 Connector x8 Link x4 operation x8 operation Not allowed x16 Connector x8 Link x4 operation x8 operation x8 operation x16 Connector x16 Link x4 operation x8 operation x16 operation 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 4 For additional information about PCI Express technology, see the technology brief titled "HP local I/O strategy 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 "Serial Attached SCSI technology" available at http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00301688/c00301688.pdf. 7