In this article, I'll share a few of my tips for building a PowerHA™ cluster within a virtual I/O (VIO) environment. I'll briefly describe an LPAR and VIO server (VIOS) design and layout for a simple two-node PowerHA cluster. However, I won't go into specific PowerHA configuration, as that topic is too large to cover in detail here. For in-depth information, I'll refer you to the official IBM PowerHA documentation (see Resources). This article also assumes that you have experience with AIX®, VIO, and PowerHA.
The example environment covered by this article consists of two POWER6® 595 servers. Each 595 is configured with dual VIO servers for redundancy, and a two-node cluster has been built across the two physical frames, that is, one PowerHA node resides on each Power 595 server. The LPARs are running AIX 5.3 TL7 SP5 with PowerHA 188.8.131.52. Each VIOS was built with version 184.108.40.206-FP11.1 across the virtual I/O landscape. Figure 1 shows this configuration.
Figure 1. PowerHA cluster overview
In the following sections, I will briefly touch on the virtual network and virtual (shared) storage configuration for the cluster nodes. In particular, I will highlight these areas:
- PowerHA boot and service network and addresses
- Shared Ethernet Adapter (SEA) configuration for the PowerHA network
- Shared volume group considerations
The virtual network configuration is an important aspect of the PowerHA configuration. Figure 2 shows how the VIOS network is configured; in this example, on one 595 frame. The VIOS network configuration is duplicated on the second frame. (Click to view a larger image.)
Figure 2. VIOS network overview
As shown in Figure 2, there are PowerHA and non-HA LPARs as clients of the same VIOS pair. You'll also notice multiple SEAs, that is, one per VLAN and usage type: PUBLIC, BACKUP, and PowerHA. Each VLAN has a unique IP range: PUBLIC 10.2.2, BACKUP 10.3.3 and PowerHA 10.1.1. There's also an interface on each LPAR, on the 10.4.4 network that is used for internal (private) communication between the LPARs over the POWER Hypervisor virtual network.
The HA nodes communicate with the outside world through VLAN40 (PVID40/41), which is the PowerHA network. The non-HA LPARs communicate through VLAN10 (PVID10), over the PUBLIC network. There's also another SEA in each VIOS, on VLAN20, which is used as a dedicated VLAN for backups over the network, hence the network name BACKUP.
Shared Ethernet Adapter failover (SEA FO) is configured for both the PUBLIC and BACKUP networks. There is no SEA FO for the PowerHA network. If a SEA fails on a VIOS, for the PowerHA network, then the service IP will move to the other boot adapter, served by the redundant VIOS.
There's no VLAN tagging in use for any of the SEAs. There's no need, as there is only a handful of VLANs to deal with in this network. However, your requirements may differ.
When viewing the PowerHA cluster network, with the
cltopinfo command, the Network
definitions on each node are as follows:
Listing 1. Network definitions
# cltopinfo Cluster Name: CLUSTER-A Cluster Connection Authentication Mode: Standard Cluster Message Authentication Mode: None Cluster Message Encryption: None Use Persistent Labels for Communication: No There are 2 node(s) and 3 network(s) defined NODE aix01adm: Network net_diskhb_01 aix01adm_hdisk1_01 /dev/hdisk1 Network net_ether_01 aix01adm 10.2.2.8 Network net_ether_02aix01 10.1.1.12 aix01b2v1 10.1.1.76 aix01b1v2 10.1.1.140 NODE aix02adm: Network net_diskhb_01 aix02adm_hdisk1_01 /dev/hdisk1 Network net_ether_01 aix02adm 10.2.2.15 Network net_ether_02 aix01 10.1.1.12 aix02b1v3 10.1.1.77 aix02b2v4 10.1.1.141 Resource Group HARG1 Startup Policy Online On Home Node Only Fallover Policy Fallover To Next Priority Node In The List Fallback Policy Never Fallback Participating Nodes aix01adm aix02adm Service IP Label aix01
As you can see, the service and boot adapters are all in the same subnetted (segmented) IP
b1v1 defines the first boot adapter (b1) associated with the first VIOS
(v1) and so on. The service address is the
adm appended to it.
Listing 2. Service and boot adapters
Service address: aix01 10.1.1.12 Netmask 255.255.255.192 IP range 10.1.1.1 - 62 boot1 address: aix01b1v1 10.1.1.76 Netmask 255.255.255.192 IP range 10.1.1.65 - 126 boot2 address: aix01b2v2 10.1.1.140 Netmask 255.255.255.192 IP range 10.1.1.129 - 190 boot1 address: aix02b1v3 10.1.1.77 Netmask 255.255.255.192 IP range 10.1.1.65 - 126 boot2 address: aix02b2v4 10.1.1.141 Netmask 255.255.255.192 IP range 10.1.1.129 - 190
Typically, when configuring a SEA on a VIOS, you would deploy SEA Fail Over to ensure network connectivity was protected in the event of a VIOS failure. However, in this PowerHA environment, the approach is different. SEA FO is not used for the PowerHA network. This way, PowerHA is aware of, and controls, network failure and failover. In this case, there is one SEA for the PowerHA network in each VIOS. If a VIOS fails, the service address moves to the boot adapter served by the redundant VIOS.
The main driver for this approach is the way the PowerHA cluster communicates in a virtual network environment. If SEA FO was configured and a failure occurred, HA would have no way of detecting the failure. Likewise, if all communication at the physical layer was lost, HA would continue to think the network was OK, as it is still able to route traffic across the virtual LAN on the Hypervisor.
This is why it is important to configure the netmon.cf file on all nodes in the cluster.
This file instructs HA on how to determine when it has lost connectivity with the network or its partner HA nodes. If this file is not configured appropriately, network failures could go undetected by PowerHA.
The netmon.cf file and VIO
There are two APARS that I recommend you review in relation to configuring the netmon.cf file in a VIO environment. You'll soon understand why this file is important and when it should be implemented.
APAR IZ01331 describes the scenarios of using VIO with PowerHA clusters and the challenges faced in detecting network failures. For example, if an "entire CEC is unplugged from the network, the PowerHA node on that Frame does not detect a local adapter down event, because traffic being passed between the VIO clients (on the same frame) looks like normal external traffic from the perspective of the LPAR's OS."
To get around this problem, the netmon.cf file is used to allow customers to declare that a given adapter should only be considered up if it can ping a set of specified targets.
If the VIOS has multiple physical interfaces on the same network or if there are two or more PowerHA nodes using one or more VIOS in the same frame, PowerHA will not be informed of (and hence will not react to) individual physical interface failures.
In the extreme case where all physical interfaces managed by VIO Servers have failed, the VIOS will continue to route traffic from one LPAR to another in the same frame, the virtual ethernet interface used by PowerHA will not be reported as having failed, and PowerHA will not react.
Each node in the cluster has a custom netmon.cf file that lists all the IP addresses it
must be able to ping for it to mark an interface up or down. For
aix01adm resides on Frame 1 (595-1) and
aix02adm resides on Frame 2 (595-2). If all network
connectivity was lost for all physical interfaces on all VIOS on 595-1, then
aix01adm would still continue functioning, as it would still be able to route packets over the virtual network. For this node (and others) to detect the problem, you populate the netmon.cf file with addresses it should be able to reach on specific interfaces. If it can't, then those interfaces are marked as down and PowerHA is able to react accordingly.
APAR IZ01874 clarifies how to choose IP addresses for the netmon.cf file. This file
should contain remote IP addresses and host names that are not in the cluster
configuration that can be accessed through the PowerHA network interfaces. These addresses must be preceded by
Some good choices for targets are name servers (DNS servers) and gateways (routers), or reliable external IP addresses (such as NTP servers) that will respond to a ping. You can use the following ping command to verify that a ping will be answered on a specific interface:
# ping -S <Boot IP address> <IP addr in netmon.cf>
<Boot IP address> is the IP address configured on the boot interface. For example,
Listing 4. ping command response on a specific interface
# ping -c5 -S aix01b1v1 aix02b1v3 PING bxaix04b1v1: (10.1.1.77): 56 data bytes 64 bytes from 10.1.1.77: icmp_seq=0 ttl=255 time=0 ms 64 bytes from 10.1.1.77: icmp_seq=1 ttl=255 time=0 ms 64 bytes from 10.1.1.77: icmp_seq=2 ttl=255 time=0 ms 64 bytes from 10.1.1.77: icmp_seq=3 ttl=255 time=0 ms 64 bytes from 10.1.1.77: icmp_seq=4 ttl=255 time=0 ms ----aix02b1v3 PING Statistics---- 5 packets transmitted, 5 packets received, 0% packet loss round-trip min/avg/max = 0/0/0 ms
Listing 5 shows some netmon.cf samples from two nodes, on two different physical frames.
Listing 5. netmon.cf samples
HOST: aix01adm 595-1 -------------------- # Care is required when modifying this file! # The nature of the VIO/PowerHA environment means the contents # of netmon.cf on each cluster node is different. # IP labels/addresses on virtual interfaces in any VIO client LPAR # within this server frame, must be excluded from this file! !REQD aix01b1v1 10.2.2.1 !REQD aix01b2v2 10.2.2.1 !REQD aix01b1v1 10.1.1.1 !REQD aix01b2v2 10.1.1.1 !REQD aix01b1v2 10.1.1.77 !REQD aix01b2v2 10.1.1.141 !REQD aix01b1v1 aix02b1v3 !REQD aix01b2v2 aix02b2v4 !REQD aix01b1v1 10.1.9.2 !REQD aix01b2v2 10.1.9.3 10.2.2.1 10.1.9.2 10.1.9.3 ntp-srvr ntp-srvr HOST: aix02adm 595-2 -------------------- # Care is required when modifying this file! # The nature of the VIO/PowerHA environment means the contents # of netmon.cf on each cluster node is different. # IP labels/addresses on virtual interfaces in any VIO client LPAR # within this server frame, must be excluded from this file! !REQD aix02b1v3 10.2.2.1 !REQD aix02b2v4 10.2.2.1 !REQD aix02b1v3 10.1.1.1 !REQD aix02b2v4 10.1.1.1 !REQD aix02b1v3 10.1.1.76 !REQD aix02b2v4 10.1.1.140 !REQD aix02b1v3 aix01b1v1 !REQD aix02b2v4 aix01b2v2 !REQD aix02b1v3 10.1.9.2 !REQD aix02b2v4 10.1.9.3 10.2.2.1 10.1.9.2 10.1.9.3 ntp-srvr ntp-srvr
If you take one line as an example,
!REQD aix01b1v1 aix02b1v3
!REQD tag specifies that the adapter (aix01b1v1)
will only be considered up if it can ping the target (aix02b1v3). The
aix01b1v1 entry specifies
which interface to use for the test, that is, aix01b1v1 resolves to 10.1.1.76, which
is the address on the en2 interface. This interface will be considered up if it is able to ping the target, aix02b1v3.
Listing 6. Determining adapter hostname
en2 will be used to connect to aix02b1v3, which is an interface on its partner node on 595-2. If it cannot communicate, the interface en2 (aix01b1v1) will be marked as down. Do not include any nodes in this file that exist on the same frame. All entries should be for systems that reside outside of the physical frame to ensure the detection of real, physical network failures to the outside world on the physical (not virtual) network.
Be careful not to specify an interface name in the netmon.cf file, such as:
!REQD en2 10.1.1.10
Including the interface name will not work in a VIO environment. The last time I
checked, there was a Design Change Request (DCR) in with the HA development team to
overcome this issue. Some customers have experienced a slow takeover due to the way
RSCT (netmon) determines if the second field in netmon.cf is an IP/hostname or the
name of an interface. In some cases, netmon will attempt to resolve the IP address of
the hostname, for example,
$ host en2, which will fail. IBM
development is working on a new algorithm to prevent interface names from being
treated as host names, especially for obvious formats such as enX. For now it's best
to eliminate the use of the interface name, for example, enX, in the netmon.cf file.
It's recommended to only use the netmon.cf method if it is appropriate in your VIO environment. Using this method changes the definition of a so-called good adapter from,"Am I able to receive any network traffic?" to "Can I successfully ping certain addresses? (regardless of how much traffic I can see)".
This can make it more likely for an adapter to be falsely considered down. If you must use this new function, I recommend that you include as many targets as possible for each interface you need to monitor.
Virtual (shared) storage
The IBM technical documentation relating to PowerHA and Virtual SCSI (VSCSI) clearly defines the supported storage configuration in a VIO environment. The shared volume group (VG) must be defined as "Enhanced Concurrent Mode." In general, Enhanced Concurrent Mode is the recommended mode for sharing volume groups in PowerHA clusters. In this mode, the shared volume groups are accessible by multiple PowerHA nodes, which results in faster failover (disk takeover) in the event of a node failure. All volume group administration on these shared disks is done from the PowerHA nodes, not from the VIOS.
In the example environment, running
lspv on the primary node confirms the shared volume group is in concurrent mode.
Listing 7. Running lspv on the primary node
root@aix01adm / # lspv hdisk0 00c79a70a6858137 rootvg hdisk1 00c79a70a20c321c sapvg concurrent
Figure 3 shows that there are two volume groups on each node. Each node has its own (non-shared) root volume group (
Figure 3. VIOS VSCSI overview
The primary node has ownership of the shared volume group as it is varied-on and
active. I can confirm this by running the
lsvg command on
the primary and taking note of some its characteristics. The
STATE is active,
VG Mode is Concurrent,
Concurrent is set to Enhanced-Capable, and
VG PERMISSION is read/write. The logical volumes in the shared volume group are open.
Listing 8. Running lsvg on the primary node
File systems on the standby nodes are not mounted until the point of failover, so
accidental use of data on standby nodes is not possible. On the standby node, it has
access to the shared enhanced-concurrent volume group, but only in a passive,
read-only mode. The
VG PERMISSION is set to passive-only. The logical volumes in the shared volume group are closed.
Listing 9. Standby nodes
root@aix02adm / # lsvg sapvg VOLUME GROUP: sapvg VG IDENTIFIER: 00c79a6000004c0000000123a2278720 VG STATE: active PP SIZE: 64 megabyte(s) VG PERMISSION: passive-only TOTAL PPs: 6398 (409472 megabytes) MAX LVs: 256 FREE PPs: 1596 (102144 megabytes) LVs: 13 USED PPs: 4802 (307328 megabytes) OPEN LVs: 0 QUORUM: 2 (Enabled) TOTAL PVs: 1 VG DESCRIPTORS: 2 STALE PVs: 0 STALE PPs: 0 ACTIVE PVs: 1 AUTO ON: no Concurrent: Enhanced-Capable Auto-Concurrent: Disabled VG Mode: Concurrent Node ID: 1 Active Nodes: 2 MAX PPs per VG: 32512 MAX PPs per PV: 4064 MAX PVs: 8 LTG size (Dynamic): 256 kilobyte(s) AUTO SYNC: no HOT SPARE: no BB POLICY: relocatable root@aix02adm / # lsvg -l sapvg sapvg: LV NAME TYPE LPs PPs PVs LV STATE MOUNT POINT oraclelv jfs2 192 192 1 closed/syncd /oracle sapmnt_CG1lv jfs2 144 144 1 closed/syncd /sapmnt usrsap_CG1lv jfs2 144 144 1 closed/syncd /usr/sap oraclestagelv jfs2 128 128 1 closed/syncd /oracle/stage sapreorg_CG1lv jfs2 64 64 1 closed/syncd /oracle/CG1/sapreorg sapbackup_CG1lv jfs2 16 16 1 closed/syncd /oracle/CG1/sapbackup mirrlogA_CG1lv jfs2 8 8 1 closed/syncd /oracle/CG1/mirrlogA mirrlogB_CG1lv jfs2 8 8 1 closed/syncd /oracle/CG1/mirrlogB origlogA_CG1lv jfs2 8 8 1 closed/syncd /oracle/CG1/origlogA origlogB_CG1lv jfs2 8 8 1 closed/syncd /oracle/CG1/origlogB sapdata1_CG1lv jfs2 1600 1600 1 closed/syncd /oracle/CG1/sapdata1 oraarch_CG1lv jfs2 80 80 1 closed/syncd /oracle/CG1/oraarch loglv01 jfs2log 1 1 1 closed/syncd N/A
bos.clvm.enh fileset must be installed (on all nodes in the cluster) to support enhanced concurrent volume groups. A new subsystem (gsclvmd) is started with enhanced concurrent volume groups. You can query this subsystem to determine the active enhanced concurrent volume groups.
Listing 10. Querying the gsclvmd subsystem
To enable a shared volume group for enhanced concurrent mode (Fast Disk Takeover), you can use CSPOC.
Listing 11. Enabling enhanced concurrent mode
# smit cl_vg Shared Volume Groups Move cursor to desired item and press Enter. List All Shared Volume Groups Create a Shared Volume Group Create a Shared Volume Group with Data Path Devices Enable a Shared Volume Group for Fast Disk Takeover Set Characteristics of a Shared Volume Group Import a Shared Volume Group Mirror a Shared Volume Group Unmirror a Shared Volume Group
Refer to the IBM technical documentation and PowerHA documentation for more information relating to PowerHA and virtual storage support.
This is just one approach to this type of configuration. I hope these brief tips provide you with some ideas on how to approach PowerHA in a VIO environment.
- Get more information on PowerHA support of VIO Server 1.5.
- Find out about the APAR: IZ01331: NEW NETMON FUNCTIONALITY TO SUPPORT HACMP ON VIO.
- Take a look at information for the APAR: IZ01874: CLARIFY HOW TO CHOOSE IP ADDRESSES FOR NETMON.C.
- Read the technical documentation on PowerHA.
- This online information describes converting volume groups to enhanced concurrent mode.
- The IBM Redbook HACMP 5.3, Dynamic LPAR, and Virtualization is practical case study about HACMP V5.3, Dynamic LPAR, and Advanced POWER Virtualization on pSeries servers.
- Take a look at the announcement for PowerHA support of VIO Server 2.1.
- Follow developerWorks on Twitter.
- Get involved in the My developerWorks community.
- Participate in the AIX and UNIX forums:
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