Datasheet

In an IBM i client partition, a VSCSI client adapter is recognized as a type 290A DCxx storage

controller device. Figure 6 depicts the VSCSI client adapter, as well as several open storage

LUNs and an optical drive virtualized by VIOS:

Figure 6: VSCSI client adapter and open storage LUNs and an optical drive as seen in IBM i.

In VIOS, a VSCSI server adapter is recognized as a vhostX device:

Figure 7: Example of VSCSI adapter seen as vhost0 by VIOS.

In VIOS, however, a new object must be created for each open storage LUN that will be

virtualized to IBM i: a virtual target SCSI device, or vtscsiX. A vtscsiX device makes a storage

object in VIOS available to IBM i as a standard DDxxx disk unit. There are three types of VIOS

storage objects that can be virtualized to IBM i:

 Physical disk units or volumes (hdiskX), which are open storage LUNs in this case

 Logical volumes (hdX and other)

 Files in a directory

For both simplicity and performance reasons, it is recommended to virtualize open storage

LUNs to IBM i directly as physical devices (hdiskX), and not through the use of logical

volumes through VIOS. (Refer to the “Performance” section for a detailed performance

discussion.) A vtscsiX device links a LUN available in VIOS (hdiskX) to a specific VSCSI adapter

(vhostX). In turn, the VSCSI adapter in VIOS is already connected to a client SCSI adapter in the

IBM i client partition. Thus, the hdiskX LUN is made available to IBM i through a vtscsiX device.

What IBM i storage management recognizes as a DDxxx disk unit is not the open storage LUN

itself, but the corresponding vtscsiX device. The vtscsiX device correctly reports the parameters

of the LUN, such as size, to the virtual storage code in IBM i, which in turn passes them on to

storage management.

Multiple vtscsiX devices, corresponding to multiple open storage LUNs, can be linked to a single

vhostX VSCSI server adapter and made available to IBM i. It is possible to virtualize up to 16

LUNs to IBM i through a single VSCSI connection. This is an IBM i limit, not VIOS. Each LUN

typically uses multiple physical disk arms in the open storage subsystem. If more than 16 LUNs

are required in an IBM i client partition, an additional pair of VSCSI server (VIOS) and client (IBM

i) adapters must be created in the HMC/SDMC or on the IVM/VIOS command line. Additional