IBM AIX HACMP SG24-5131-00 Hardware User Manual page 210

The VSDs in this scenario are mapped to the raw logical volumes lv_X and
lv_Y. Node X is a client of Node Y's VSD, and vice versa. Node X is also a
direct client of its own VSD (lv_X), and Node Y is a direct client of VSD lv_Y.
VSD configuration is flexible. An interesting property of the architecture is
that a node can be a client of any other node's VSD(s), with no dependency
on that client node owning a VSD itself. You could set up three nodes with
powerful I/O capacity to be VSD servers, and ten application nodes, with no
disk other than for AIX, PSSP, and the application executables, as clients of
the VSDs on these server nodes.
VSDs are defined in the SDR and managed by either SP SMIT panels or the
VSD Perspective. VSDs can be in one of five states as shown in Figure 18 on
page 192.
Figure 18. VSD State Transitions
This figure shows the possible states of a VSD and the commands used to
move between states. VSD configuration changes, or manual recovery of a
failed VSD, require you to move the VSD between various states.
The distributed data access aspect of VSD scales well. The SP Switch itself
provides a very high-bandwidth, scalable interconnect between VSD clients
and servers, while the VSD layers of code are efficient. The performance
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Undefined
define
Defined
cfgvsd
Stopped
preparevsd
Suspended
resumevsd
Active
Available
undefine
VSD information is
available in the SDR
cfgvsd
Open/close and I/O
requests fail
stopvsd
I/O requests queued and
open/close request serviced
suspendvsd
Open/close and
I/O requests serviced