An Introduction to the New IBM eServer pSeries High Performance Switch

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.