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Added by OneSkyWalker, last edited by OneSkyWalker on Aug 17, 2009  (view change)
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p6 520 split backplane and internal SAS RAID

On a p6 520, the DASD/Media Backplane without external SAS (feature code 8341) provides:

  • six hot-swappable 3.5-inch SAS disk bays, one hot-plug, slim-line media bay, and one 5.25 inch media bay and
  • one integrated SAS DASD controller with eight SAS ports which are connected to the six disk bays and to any media devices.

On servers with a feature code 8341 backplane, all six SAS disk bays and the media devices must be assigned to the same LPAR. And with this backplane, there is no support of hardware RAID by the integrated SAS DASD controller.


On a p6 520, the optional DASD/Media Backplane with external SAS port (feature code 8345) provides:

  • six hot-swappable 3.5-inch SAS disk bays, one hot-plug, slim-line media bay, and one 5.25 inch media bay and
  • one integrated SAS DASD controller with eight SAS ports which are connected to the six disk bays and to any media devices.

On servers with a feature code 8345 backplane, there is the opportunity to order additional features which provide additional functionality:

  • Optional SAS Cable, DASD Backplane (Split) to Rear Bulkhead (feature code 3670), which allows three of the six SAS disk bays to be accessed via an external SAS port on the back of the p6 520. Feature code 3670 requires that a SAS Cable (feature code 3679) and a PCI-X SAS controller (feature code 5900 or 5912) also be configured. When the SAS Cable (FC 3679) is used to connect the PCI-X SAS controller to the external SAS port provided by feature code 3670, then three disk bays (accessed via the PCI-X SAS controller) can be assigned to one LPAR and three disk bays (accessed via the integrated SAS controller) can be assigned to another LPAR.

    Any media devices continue to be accessed via the integrated SAS controller.

    A PCI-X SAS controller (feature code 5900 or 5912, both of which are CCIN 572A) supports RAID 0, 5, 6, 10, but because the controller has no write cache, RAID 5 or 6 arrays will exhibit very poor write performance. Since base AIX provides striping and/or mirroring (software RAID 0, 1, or 10), software RAID is perhaps a better choice than the hardware (SAS) RAID 0 & 10 arrays provided by CCIN 572A, simply because most AIX sysadmins are typically more familiar with software RAID. To configure hardware RAID on CCIN 572A, use the IBM SAS Disk Array Manager, as described in the Power Systems SAS RAID controllers for AIX nanual (downloadable from the PDF files for the 8203-E4A (IBM Power 520) web page).

    Feature code 5902 (CCIN 572B, PCI-X DDR Dual - x4 3Gb SAS RAID Adapter) is not a viable option for integrated disks with a split backplane. Two such adapters are required to provide redundant write cache, both connected to the same set of disks. Integrated disks with a split backplane can be connected to only one adapter.
  • Optional SAS Cable, DASD Backplane to Rear Bulkhead (feature code 3674), which connects the integrated SAS DASD controller to an external SAS port on the back of the p6 520. If an external EXP 12S expansion drawer (feature code 5886) is connected to the external SAS port provided by feature code 3674, then the integrated SAS DASD controller can access the twelve SAS disk bays in the EXP 12S in addition to the six SAS disk bays in the p6 520.

    (For information about cabling a 5886 SAS drawer to a Power System server, please see Chapter 9, "Connecting the 5886 SAS disk-drive enclosure" in the Expansion Units and Disk-Drive Enclosures manual and the Serial attached SCSI cable planning section of Chapter 10, "Planning for cables" in the Site and Hardware Planning Guide, both of which are downloadable from the PDF files for the 8203-E4A (IBM Power 520) web page.)

    Feature code 3674 can not be configured in a 1-core p6 520 (feature code 5633).
  • Optional SAS RAID Enablement (feature code 5679 and CCIN 57B8), which allows RAID 0, 5, 6, or 10 arrays to be configured on the integrated SAS DASD controller. If feature code 3674 is selected and an external EXP 12S expansion drawer is connected, up to eighteen SAS disk drives can be configured with hardware RAID. If feature code 3670 is selected, implying that at most three drives are accessible by the integrated SAS DASD controller, then RAID options are limited to 1 and 5.

    To configure hardware RAID on CCIN 57B8, use the IBM SAS Disk Array Manager, as described in the Power Systems SAS RAID controllers for AIX manual (downloadable from the PDF files for the 8203-E4A (IBM Power 520) web page).

    The SAS RAID Enablement feature provides redundant write caches so there is no requirement that a second RAID adapter be connected to the same set of disks.

As an alternative to hardware RAID, AIX striping and/or mirroring (software RAID 0, 1, or 10) can be used with any hardware configuration which provides a sufficient number of hdisks to AIX, but AIX does not provide software RAID 5 or 6.

The Power Systems Managing PCI Adapters manual (downloadable from the PDF files for the 8203-E4A (IBM Power 520) web page) defines the relationship between Custom Card Identification Number (CCIN) and feature code.

The contents of this web page solely reflect the personal views of the authors and do not necessarily represent the views, positions, strategies or opinions of IBM or IBM management. Please use the Add Comment link at the bottom of the page to provide feedback. Note: Until you log in (using the link in the upper right corner of this web page), you will not see the Add Comment link and you can not add a comment. If you do not already have an IBM ID, use the Register Now link on the sign in page to obtain one. Registration is quick and easy.

The contents of this web page are loosely based on the 8203-E4A Power System LPAR Internal booting and RAID capabilities Techdoc published by Carlos Inigo Ladron De Guevara, but he is not responsible for this web page nor its contents.

 
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