Special planning considerations for auxiliary write cache I/O adapters

Two auxiliary write cache I/O adapter features are available for IBM® eServer™ i5 and System i® servers that enhance data integrity and continuity by providing two complete nonvolatile copies of write cache data.

To help you plan and implement a data integrity solution that includes the auxiliary write cache feature, see the Planning for Disk Storage Protection with Auxiliary Write Cache Solutions redpaper. Use the redpaper to learn more about what the auxiliary write cache feature is and what it does. The redpaper also helps you plan for implementing auxiliary write cache on your servers and provides references and links to other documentation.

You need to consider and plan for the following points prior to ordering, because the additional IOA space required may require the purchase of another expansion unit:

• The auxiliary write cache is an additional I/O adapter (IOA) that requires a slot of its own.
• The auxiliary write cache IOA has a one-to-one relationship with a disk IOA. The pair of IOAs is sometimes referred to as the primary IOA (disk IOA) and the secondary IOA (auxiliary cache IOA).
• The two IOAs must be in the same enclosure.
• The two IOAs must be in the same logical partition.
• The two IOAs are cabled directly together by a SCSI cable on a dedicated SCSI bus that runs in Ultra3 mode (U320).
• The cable attaches to the SCSI port on the secondary IOA and to the fourth SCSI port on the primary IOA.
• If all four SCSI ports on the primary IOA are already being used, you need to determine how to free up the fourth SCSI port. You could use all four ports if there are more than 15 disk drives that are attached to the disk IOA. In this situation, you need to move the cable and you might have to move disk drives.
• If there are not enough open PCI slots in an enclosure for the desired quantity of auxiliary write cache IOAs, you need to determine what other IOAs can be moved to provide open PCI slots, and where the displaced adapters can be reinstalled.
  Attention:

  • The need to move disk drives or a cable may also require the stopping and restarting of device parity protection (RAID).
  • Moving adapters or disk drives to provide open PCI slots or SCSI ports in the same partition or enclosure might change the configuration of logical partitions.
• The auxiliary write cache IOA is only supported with the #2757 PCI-X Ultra RAID Disk Controller and #2780 PCI-X Ultra4 RAID Disk Controller IOAs.
• The two feature codes for the auxiliary write cache IOA are #5580 and #5581.
  • #5580 is the #2780 PCI-X Ultra4 RAID Disk Controller with an auxiliary write cache IOA
  • #5581 is the #2757 PCI-X Ultra RAID Disk Controller with an auxiliary write cache IOA.
• The System i5® models that support the #5580 and #5581 are the 270, 520, 550, 570, 595, 800, 810, 820, 825, 830, 840, 870 and 890. The basic placement rule is that #5580 and #5581 are supported anywhere a #2780 or #2757 are supported. For more information, see the PCI Placement Rules for the IBM eServer i5 and iSeries® Servers with i5/OS® V5R3 redpaper.
  Note: The auxiliary write cache IOA cannot be placed in the system units of the Models 520, 550 and 570. On those models the auxiliary write cache IOA needs to be placed in the I/O unit on your system.
• The auxiliary write cache IOA is supported on the System i5 servers under i5/OS and OS/400® only. i5/OS V5R3 or later is required to support auxiliary write cache. Support for OS/400 V5R2 will be added at a later date. There are also additional PTFs that are needed to support the auxiliary write cache IOA for both V5R3 and V5R2. See the IBM eServer Prerequisite Web site.
• AIX® and Linux® do not support the auxiliary write cache IOA.