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Understand your options for 12X PCIe I/O drawers

Understand your options for 12X PCIe I/O drawers

The 12X PCI Express (PCIe) I/O drawers are popular for expanding the I/O capabilities of Power Systems servers. This article provides an overview of the configuration options for the PCIe adapter slots and serial-attached SCSI (SAS) disk bays.

Drawer Highlights

There are two versions of the 12X PCIe I/O drawer, which are ordered as Power Systems server feature codes. Drawer feature 5802 has 10 PCIe hot-plug adapter slots and 18 SAS disk drive bays. Drawer feature 5877 has 10 PCIe hot-plug adapter slots and no disk bays. Note that feature 5877 can’t be upgraded to add the SAS disk bays.

12X PCIe I/O drawer characteristics:

  • 10 PCIe hot-plug adapter slots with blind-swap cassettes
  • 18 SAS small form factor (SFF) hot-swap disk bays (feature 5802, only)
  • 19-inch wide and 4 EIA units (4U) tall
  • Redundant power supplies, standard
  • Connected to host server using a 12X loop
  • Up to two drawers supported per 12X loop

SAS Disk Bay Configuration

The feature 5802 version of the 12X PCIe I/O Drawer has 18 disk bays that can be configured into one, two or four separate groups. This allows you to divide the disk bays to meet specific configuration needs. The disk groups are internally connected to a set of four SAS connection ports on the back of the drawer. The disk bay configuration is set using a small switch located on the back of the drawer. If you change the switch setting, the drawer must be power-cycled for the drive bays to be reconfigured. SAS disk bay configuration support varies by operating system, as shown in Table 1.

There are no integrated SAS controllers inside the drawer. To access the disk drives, you’ll need to install a SAS PCIe adapter into one of the PCIe slots within the same drawer where the disk drives are located. n external SAS cable is used to connect the SAS adapter card to the SAS ports on the back of the drawer.

If you choose to divide the disk bays into multiple groups, you’ll need an available SAS port and cable for each disk group you plan to use. At least one SAS disk drive must be installed in each disk group that is cabled to a SAS adapter. A single, four-port SAS adapter can be cabled to multiple disk groups. Remember all of the SAS ports associated with a SAS adapter will belong to a single partition. Be sure to configure additional SAS adapters if you have more than one partition that will need disk access.

The last item to cover is the mapping of the disk groups to the SAS connection ports on the back of the drawer. Figure 2 shows the internal connection paths when the partition switch is set to “1” which results in one group of 18 disk bays. The primary connection will be from a SAS adapter port to SAS port 1 on the back of the drawer. You can create a second path to the drive group by connecting a SAS adapter port to SAS port 4. The second path can use the same SAS adapter as the primary connection or you can use a different SAS adapter. The adapter providing the second path connection must be located in the same drawer as the drive group it’s connected to.

Figure 3 shows the internal connection paths for partition switch position “2,” which establishes two groups each with nine disk bays. The primary connections to the two disk groups will be from SAS adapter ports to SAS ports 1 and 3 on the back of the drawer. Second path connections are available through SAS ports 2 and 4.

Figure 4 shows the last configuration option, with the partition switch set to “4.” This configuration provides four disk groups. Each of the four SAS ports on the back of the drawer acts as a primary connection point. With this configuration, there’s no option for a second path connection to any of the disk groups.

For detailed examples of primary and second path cabling examples between the SAS adapters and the SAS ports, please review the Enclosures and Expansion Units document. Last, be sure to order the appropriate quantity of SAS adapters and external SAS cables to support the number of partitions that will need to access the disk drives in the drawer.

The 12X PCIe I/O drawers are supported on the following Power Systems servers: POWER6 models 520, 550, 560, and 570; POWER7 models 720, 740, 750, 770, and 780.

Adapter-Slot Overview

The 10 PCIe hot-plug slots feature blind-swap cassette technology. The blind-swap cassette allows you to hot swap adapter cards without sliding the I/O drawer out of the rack. Each blind-swap cassette slides in from the back of the I/O drawer and then locks down into place. his simplifies system installation and serviceability because it isn’t necessary to use cable-management arms to handle the extra cable that would be required if the drawer had to be pulled out on slides to service the adapter cards.

Now let’s take a look at the PCIe slots layout, shown in Figure 1. PCIe slot groups 1 and 2 each have their own PCIe hub with direct connections to the drawer controller. Note that the PCIe hub for slot group 3 doesn’t have a direct connection the drawer controller. At the bottom of the diagram, the preferred placement order for high-performance adapters is shown.

Charlie Cler supports customers in a solutions-architect role at Forsythe Technology Inc. He can be reached at

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