102 An Introduction to the New IBM Eserver pSeries High Performance Switch
3.4 IBM Virtual Shared Disks
This section contains a short description of the IBM Virtual Shared Disks 4.1 product in a
pSeries High Performance Switch environment.
In this section we include the following topics:
VSD overview
Recovery scenarios
Restrictions for VSD
IBM Subsystem Device Driver (SDD) overview
High Performance Switch considerations and tuning recommendations
3.4.1 Overview of the Virtual Shared Disk components
IBM Virtual Shared Disk is a subsystem that lets application programs that are running on
different nodes of an RSCT peer domain access a raw logical volume as if it were local at
each of the nodes. Each Virtual Shared Disk corresponds to a logical volume that is actually
local at one of the nodes, which is called the server node.
The Virtual Shared Disk subsystem routes I/O requests from the other nodes, called client
nodes, to the server node and returns the results to the client nodes. The I/O routing is done
by the Virtual Shared Disk device driver that interacts with the AIX Logical Volume Manager
(LVM). The device driver is loaded as a kernel extension on each node. Thus, raw logical
volumes can be made globally accessible in the VSD nodeset (domain).
The application program interface to a Virtual Shared Disk is the raw device (or device special
file). This means application programs must issue requests to a Virtual Shared Disk using the
block size specified by the LVM (currently, requests are multiples of 512 bytes on 512-byte
block boundaries). Figure 3-15 shows a logical view of the the VSD subsystem.
Figure 3-15 Logical view of the VSD subsystem
3.4.2 Product packaging
VSD used to be a component of the PSSP, and only SP customers could take advantage of it.
VSD is now shipped as part of the RSCT Release 2.3, included with the AIX 5L operating
system. It can also be installed as a PTF to AIX Version 5.2.B (AIX 5.2 maintenance level 2).
VSD packaging is described in Table 3-3 on page 103.
LVM
IP
VSD
LVM
IP
VSD
LVM
IP
VSD
Node 1
Node 2
Node n
LV
VG
PV
PV
Chapter 3. Application considerations 103
Table 3-3 VSD filesets
3.4.3 Configuration repository
In previous releases of VSD, the configuration data for nodes and drives was stored in the
SDR database of PSSP. Starting with Version 4.1, VSD comes with RSCT. All configuration
data is stored in appropriate RSCT classes.
The VSD product brings four new classes to the RSCT repository:
IBM.vsdnode
IBM.vsdtable
IBM.vsdgvg
IBM.rvsdrestrictlevel
You can gather the information on these subclasses with the lsrsrc -ls command. You
tipically will not change entries in these classes manually. They are managed by appropriate
VSD commands. These entries can be modified using the standard RSCT command chrsrc.
IBM.vsdnode
This class contains node-related information such as the communication interface and IP
address. Each node has its own stanza in this class. Example 3-5 is a sample of the class
contents.
Example 3-5 Contents of IBM.vsdnode class
resource 1:
VSD_nodenum = 1
VSD_adapter = "ml0"
VSD_min_buddy_buffer_size = 4096
VSD_max_buddy_buffer_size = 262144
VSD_max_buddy_buffers = 128
VSD_maxIPmsgsz = 61440
RVSD_version = 0
CVSD_cluster_name = ""
CVSD_node_number = 0
cvgs_defined = 0
VSD_ipaddr = "10.10.10.11"
NodeNameList = {"p690_LPAR1.itso.ibm.com"}
resource 2:
VSD_nodenum = 2
VSD_adapter = "ml0"
VSD_min_buddy_buffer_size = 4096
VSD_max_buddy_buffer_size = 262144
VSD_max_buddy_buffers = 128
VSD_maxIPmsgsz = 61440
RVSD_version = 0
CVSD_cluster_name = ""
CVSD_node_number = 0
cvgs_defined = 0
VSD_ipaddr = "10.10.10.12"
Fileset Name Description
rsct.vsd.vsdd VSD device driver
rsct.vsd.rvsd Recoverable VSD
rsct.vsd.cmds VSD commands
rsct.vsd.vsdrm VSD resource manager
104 An Introduction to the New IBM Eserver pSeries High Performance Switch
NodeNameList = {"p690_LPAR2.itso.ibm.com"}
...
IBM.vsdtable
This class contains information about VSD storage objects. Each VSD storage object has its
own entry as a separate stanza. See Figure 3-6 for a sample of the class contents.
Example 3-6 Contents of IBM.vsdtable class
resource 1:
VSD_name = "gpfs0vsd"
global_group_name = "gpfs0gvg"
logical_volume_name = "gpfs0lv"
minor_number = 5
size_in_MB = 43840
lv_blk0_pdev = 3342340
lv_blk0_pbn = 4352
resource 2:
...
IBM.vsdgvg
This class contains data related to global VSD volume groups. Example 3-7 shows the
sample contents of this class.
Example 3-7 Contents of IBM.vsdgvg class
resource 1:
global_group_name = "gpfs0gvg"
local_group_name = "gpfs0vg"
primary_node = 1
secondary_node = 2
eio_recovery = 1
recovery = 0
primary_ts = ""
secondary_ts = ""
server_list = "0"
vsd_type = "VSD"
resource 2:
...
IBM.rvsdrestrictlevel
This class contains usually one entry describing the level of VSD software agreed by all
nodes in the cluster. Example 3-8 shows the entry for VSD 4.1.
Example 3-8 Contents of IBM.rvsdrestrictlevel class
resource 1:
level = "4010000"
3.4.4 Shared external disk access
The Virtual Shared Disk subsystem supports two methods of external disk access: serial
(non-concurrent) and concurrent. Figure 3-16 on page 105 presents an example VSD
network implementation.

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