POWER Hypervisor Virtual I/O Server 1 IBM i Client Partition FC adapter VFC client adapter ID10 VFC client adapter ID20 VFC server adapter ID10 Virtual I/O Server 2 VFC server adapter ID20 FC adapter * * * IBM i disk multi-pathing or mirroring for Virtual I/O Server redundancy D840 LUNs #1-n NPIV-capable SAN Switch IBM FlashSystem 900 AE3 Figure 6-6 IBM i NPIV-attachment with two redundant Virtual I/O Servers For VIOS attachment (NPIV-attachment), the Fibre Channel adapter queue depth is a storage  performance-related tunable parameter. It can be considered to be increased if not already  using VIOS version 2.2.4.10 or later and having deployed its default  rule set  for applying IBM  recommended device settings.  The Fibre Channel adapter model-dependent current setting for its adapter queue depth, its  allowed range, and its increase to its maximum supported value is shown in Example 6-4.  With the fcs X  FC adapter port resource usually in use, as implied in the example, VIOS would  still need to be restarted for the permanent change of the adapter queue depth that is made  to its resource database to become effective. Example 6-4 Displaying and changing the VIOS FC adapter queue depth $ lsdev -dev fcs0 -attr | grep num_cmd_elems num_cmd_elems 500 Maximum number of COMMANDS to queue to the adapter True $ lsdev -dev fcs0 -range num_cmd_elems 20...4096 (+1) $ chdev -dev fcs0 -perm -attr num_cmd_elems=4096 fcs0 changed For both native and VIOS NPIV-attachment, the IBM FlashSystem 900 LUNs report to IBM i  as device type D840 disk units, as shown in Figure 6-7 on page 165.  Figure 6-7 shows the disk configuration of a newly set up IBM i partition with its load source  unit, that is, disk unit 1 being the only disk unit configured in the system ASP (ASP 1). All disk  units are accessible from IBM i through two active Fibre Channel paths. The IBM i integrated  multi-path driver distributes the I/O across all active paths of a disk unit using a round-robin  algorithm with some load-balancing applied. Non-configured and non-initialized disk units,  that is, those not assigned to an IBM i ASP yet, are still reported with  DPH xxx  resource names. 164  Implementing IBM FlashSystem 900 Model AE3