IBM DS8000 manual Linux on IBM iSeries, Gaps in the LUN sequence

Example A-14shows the SCSI disk assignment after one more DS8000 volume is added.

Example: A-14 SCSi disks after dynamic addition of another DS8000 volume

/dev/sda - internal SCSI disk

/dev/sdb - 1st DS8000 volume, seen by HBA 0 /dev/sdc - 2nd DS8000 volume, seen by HBA 0 /dev/sdd - 1st DS8000 volume, seen by HBA 1 /dev/sde - 2nd DS8000 volume, seen by HBA 1 /dev/sdf - new DS8000 volume, seen by HBA 0 /dev/sdg - new DS8000 volume, seen by HBA 1

The mapping of special device files is now different than it would have been if all three DS8000 volumes had been already present when the HBA driver was loaded. In other words: if the system is now restarted, the device ordering will change to what is shown in Example A-15.See also “SCSI device assignment changes” on page 360.

Example: A-15 SCSi disks after dynamic addition of another DS8000 volume and reboot

/dev/sda - internal SCSI disk

/dev/sdb - 1st DS8000 volume, seen by HBA 0 /dev/sdc - 2nd DS8000 volume, seen by HBA 0 /dev/sdd - new DS8000 volume, seen by HBA 0 /dev/sde - 1st DS8000 volume, seen by HBA 1 /dev/sdf - 2nd DS8000 volume, seen by HBA 1 /dev/sdg - new DS8000 volume, seen by HBA 1

Gaps in the LUN sequence

The Qlogic HBA driver cannot deal with gaps in the LUN sequence. When it tries to discover the attached volumes, it probes for the different LUNs, starting at LUN 0 and continuing until it reaches the first LUN without a device behind it.

When assigning volumes to a Linux host with QLogic FC HBAs, make sure LUNs start at 0 and are in consecutive order. Otherwise the LUNs after a gap will not be discovered by the host. Gaps in the sequence can occur when you assign volumes to a Linux host that are already assigned to another server.

The Emulex HBA driver behaves differently: it always scans all LUNs up to 127.

Linux on IBM iSeries

Since OS/400 V5R1, it has been possible to run Linux in an iSeries partition. On iSeries models 270 and 8xx, the primary partition must run OS/400 V5R1 or higher and Linux is run in a secondary partition. For later i5 systems (models i520, i550, i570 and i595), Linux can run in any partition.

The DS8000 requires the following iSeries I/O adapters to attach directly to an iSeries or i5 Linux partition:

￿0612 Linux Direct Attach PCI

￿0626 Linux Direct Attach PCI-X

It is also possible for the Linux partition to have its storage virtualized, whereby a partition running OS/400 hosts the Linux partition's storage requirements. In this case, if using the DS8000, they would be attached to the OS/400 partition using either of the following I/O adapters:

￿2766 2 Gigabit Fibre Channel Disk Controller PCI

Appendix A. Open systems operating systems specifics 363