HP OpenVMS systems documentation

When any node has multiple buses connecting to the same storage device, the new HSZ allocation class shown in Figure 6-15 must be used.

Figure 6-15 Devices Named Using an HSZ Allocation Class

An HSZ allocation class is similar to the HSC, HSD, and HSJ allocation classes. The device name, using an HSZ allocation class number, takes the following form:

$HSZ-allocation-class$ddcu

where:

• HSZ-allocation-class is a decimal value from 1 to 999, assigned to a particular HSZ storage controller by the system manager
• dd represents the device class, which is DK for disk
• c represents the controller, which must be A when using an HSZ allocation class
• u represents the device unit number, which is determined by the SCSI bus ID and the logical unit number (LUN) of the device

The system manager sets an HSZ allocation class from the HSZ console, using one of the following commands, as appropriate to the configuration:

HSZ> SET THIS_CONTROLLER ALLOCATION_CLASS = n

or

HSZ> SET OTHER_CONTROLLER ALLOCATION_CLASS = n

where n is a value from 1 to 999.

When the allocation class is set on one controller module in a dual redundant configuration, it is automatically set to the same value on the other controller.

In the following example, the allocation class is set to 199. The example shows that the value is set for both controllers.

z70_B => SET THIS ALLOCATION_CLASS=199 z70_B => SHOW THIS_CONTROLLER Controller: HSZ70 ZG64100136 Firmware XB32-0, Hardware CX25 Configured for MULTIBUS_FAILOVER with ZG64100160 In dual-redundant configuration Device Port SCSI address 6 Time: NOT SET Host port: SCSI target(s) (0, 2, 3, 4, 5, 6) TRANSFER_RATE_REQUESTED = 20MHZ Host Functionality Mode = A Allocation class 199 Command Console LUN is target 0, lun 1 Cache: 32 megabyte write cache, version 4 Cache is GOOD Battery is GOOD No unflushed data in cache CACHE_FLUSH_TIMER = DEFAULT (10 seconds) NOCACHE_UPS z70_B => SHOW OTHER_CONTROLLER Controller: HSZ70 ZG64100160 Firmware XB32-0, Hardware CX25 Configured for MULTIBUS_FAILOVER with ZG64100136 In dual-redundant configuration Device Port SCSI address 7 Time: NOT SET Host port: SCSI target(s) (0, 2, 3, 4, 5, 6) TRANSFER_RATE_REQUESTED = 20MHZ Host Functionality Mode = A Allocation class 199 Command Console LUN is target 0, lun 1 Cache: 32 megabyte write cache, version 4 Cache is GOOD Battery is GOOD No unflushed data in cache CACHE_FLUSH_TIMER = DEFAULT (10 seconds) NOCACHE_UPS

The following rules pertain to the use of an HSZ allocation class in SCSI device names:

1. In multibus mode, an HSZ allocation class must be used in a device name (otherwise, the device is not configured).
2. In transparent mode, an HSZ allocation class can be used in a device name but it is not required.
3. The HSZ allocation class number must be the same for both controllers of an HSZ. This is handled automatically by the HSZ firmware.
4. The HSZ allocation class number must be unique among all types of allocation classes throughout the cluster.
5. The HSZ allocation class must be specified when referring to devices that have an HSZ allocation class. For example, the names DKA500 and NODE10$DKA500 can not be used. In addition, the $GETDVI system service will only return the fully specified name, including the HSZ allocation class, for these devices.

Figure 6-16 shows a multipath configuration with both a tape storage subsystem and a disk storage subsystem. Note that the disk storage controllers are configured in multibus mode.

Figure 6-16 Single Host With Two Dual-Ported Storage Controllers, One Dual-Ported MDR, and Two Buses

Note the following about this configuration:

• Host has two adapters, each attached to a different bus.
• Each port on each HSGx or HSVx storage controller is attached to a different interconnect.
• Each port on the Modular Data Router (MDR) or the Network Storage Router (NSR) is attached to a different interconnect.
• Both storage controllers can access the same disk.
• Host has four paths to the same logical unit.

Note that each HSG80 port has its own Fibre Channel address and Fibre Channel port WWID. This is different from an HSZ80 in multibus mode where all the ports respond to the same SCSI address and must, therefore, be connected to different SCSI buses. The separate FC addresses enable both ports of the dual HSG80 to be on the same FC.

Figure 6-17 is similar to Figure 6-16, except it has two additional Fibre Channel interconnects.

Figure 6-17 Single Host With Two Dual-Ported Storage Controllers, One Dual-Ported MDR, and Four Buses

Note the following about this configuration:

• Host has four adapters, each attached to a different interconnect.
• Each port on each HSGx or HSVx storage controller is attached to a different interconnect.
• Each port on the Modular Data Router (MDR) or the Network Storage Router (NSR) is attached to a different interconnect.
• Host has four paths to the same logical unit.

Figure 6-18 builds on the previous two figures. Instead of a single host, it has two hosts.

Figure 6-18 Two Hosts With Two Dual-Ported Storage Controllers, One Dual-Ported MDR, and Four Buses

Note the following about this configuration:

• Each host has four adapters, each attached to a different interconnect.
• Each port on each HSGx or HSVx storage controller is attached to a different interconnect.
• Each port on the Modular Data Router (MDR) or the Network Storage Router (NSR) is attached to a different interconnect.
• Each host has four paths to the same logical unit of the disk storage subsystem and two paths to the tape storage subsystem.

Parallel SCSI and Fibre Channel interconnects support multipath configurations. Implementation of these configurations is similar, and the system parameters and the command for specifying paths are the same. The syntax for the path identifiers differs.

Implementing multiple paths to devices consists of the following steps:

1. Configuring a system or systems with multiple physical paths to those devices for which you want multipath support.
2. Setting the HSx controller to multibus mode (disks only).
3. Optionally qualifying multipath support by setting certain multipath system and console parameters, as appropriate for your configuration.
4. Optionally tailoring the operation of multipath functionality, using the DCL command SET DEVICE/qualifier/PATH=path-identifier.

Figure 6-19 shows a valid multipath, multihost configuration.

Figure 6-19 Two Hosts With Shared Buses and Shared Storage Controllers

Note the following about this configuration:

• Each host has two adapters.
• Both hosts are connected to the same two buses.
• Both hosts share the storage.
• Each storage controller is connected to one bus only.
• The two storage controllers are connected to the same disks.

This configuration provides each host with two direct paths and one MSCP served path to each device.

Figure 6-20 shows a valid multipath configuration for systems that are not configured on the same bus.

Figure 6-20 Two Hosts With Shared, Multiported Storage Controllers

Note the following about this configuration:

• Each host has two adapters.
• Each host is connected to two buses but the hosts do not share a bus.
• Both hosts share the storage.
• Each storage controller has two connections, one to each host.
• The two storage controllers are connected to the same disks.

This configuration provides each host with two direct paths, one to each storage controller, and one MSCP served path to each device.

6.7.2 Invalid Multipath Configuration

Figure 6-21 shows an invalid multipath configuration. The configuration is invalid because, if multiple hosts in a cluster are connected to an HSZ or HSG, they must all have connections to the same controller modules (see Table 6-1). In this configuration, each host is connected to a different controller module.

Figure 6-21 Invalid Multipath Configuration

Multipath support is enabled and qualified by the use of the system parameters described in Table 6-3. (Certain multipath system parameters are reserved for the operating system.)

Table 6-3 Multipath System Parameters

Parameter	Description
MPDEV_ENABLE	Enables the formation of multipath sets when set to ON (1). When set to OFF (0), the formation of additional multipath sets and the addition of new paths to existing multipath sets is disabled. However, existing multipath sets remain in effect. The default is ON. MPDEV_REMOTE and MPDEV_AFB_INTVL have no effect when MPDEV_ENABLE is set to OFF.
MPDEV_LCRETRIES	Controls the number of times the system retries direct paths to the controller that the logical unit is on line to, before moving on to direct paths to the other controller, or to an MSCP served path to the device (MSCP paths apply only to disks). The valid range for retries is 1 through 256. The default is 1.
MPDEV_POLLER	Enables polling of the paths to multipath set members when set to ON (1). Polling allows early detection of errors on inactive paths. If a path becomes unavailable or returns to service, the system manager is notified with an OPCOM message. When set to OFF (0), multipath polling is disabled. The default is ON. Note that this parameter must be set to ON to use the automatic failback feature.
MPDEV_REMOTE (disks only)	Enables MSCP served paths to become members of a multipath set when set to ON (1). When set to OFF (0), only local paths to a SCSI or Fibre Channel device are used in the formation of additional multipath sets. MPDEV_REMOTE is enabled by default. However, setting this parameter to OFF has no effect on existing multipath sets that have remote paths. To use multipath failover to a served path, MPDEV_REMOTE must be enabled on all systems that have direct access to shared SCSI or Fibre Channel devices. The first release to provide this feature is OpenVMS Alpha Version 7.3--1. Therefore, all nodes on which MPDEV_REMOTE is enabled must be running OpenVMS Alpha Version 7.3--1 (or later). If MPDEV_ENABLE is set to OFF (0), the setting of MPDEV_REMOTE has no effect because the addition of all new paths to multipath sets is disabled. The default is ON.
MPDEV_AFB_INTVL (disks only)	Specifies the automatic failback interval in seconds. The automatic failback interval is the minimum number of seconds that must elapse before the system will attempt another failback from an MSCP path to a direct path on the same device. MPDEV_POLLER must be set to ON to enable automatic failback. You can disable automatic failback without disabling the poller by setting MPDEV_AFB_INTVL to 0. The default is 300 seconds.
MPDEV_D1	Reserved for use by the operating system.
MPDEV_D2	Reserved for use by the operating system.
MPDEV_D3	Reserved for use by the operating system.
MPDEV_D4	Reserved for use by the operating system.

6.7.4 Path Identifiers

The system management commands described in the following sections allow you to monitor and control the operation of multipath failover. These commands provide a path identifier to uniquely specify each path in a multipath set.

Direct Fibre Channel paths are identified by the local host adapter name and the remote Fibre Channel port WWID --- that is, the initiator and the target. For example, in Figure 6-22, the path identifier for the path from the host adapter on the left to the HSG storage controller on the left is PGB0.5000-1FE1-0000-0201. (The second port on each HSG is omitted for convenience.) You can obtain the WWID for a storage controller from its console.

Figure 6-22 Fibre Channel Path Naming

Direct parallel SCSI paths are identified by the local host adapter name and the remote SCSI bus ID --- that is, the initiator and the target. For example, in Figure 6-23, the path identifiers for node Edgar's two direct paths to the disk would be named PKB0.5 and PKC0.5.

The path identifier for MSCP served paths is MSCP .

Figure 6-23 Configuration With Multiple Direct Paths

When multipath support is enabled, you can display the multiple paths to a device using either of the following variants of the SHOW DEVICE DCL command:

SHOW DEVICE/FULL device-name SHOW DEVICE/MULTIPATH_SET device-name

The SHOW DEVICE/FULL device-name command displays the traditional information about the device first and then lists all the paths to a device by their path identifiers (described in Section 6.7.4).

The SHOW DEVICE/MULTIPATH_SET device-name command lists only some brief multipath information about devices that have multiple paths.

Multipath information is displayed only on nodes that are directly connected to the multipath device.

6.7.5.1 Displaying Paths With SHOW DEVICE/FULL

The following example shows the output of a SHOW DEVICE/FULL device-name command. Note that the use of multiple paths is shown at the beginning of the display ( device has multiple I/O paths ), and the multiple path descriptions are shown toward the end of the display, beneath I/O paths to device . Note, too, that the values for Error count and Operations completed shown at the beginning of the display are the sums of the counts for each path.

$ SHOW DEVICE/FULL $1$DGA23: Disk $1$DGA23: (WILD8), device type HSG80, is online, mounted, file-oriented device, shareable, device has multiple I/O paths, served to cluster via MSCP Server, error logging is enabled. Error count 3 Operations completed 32814199 Owner process "" Owner UIC [SYSTEM] Owner process ID 00000000 Dev Prot S:RWPL,O:RWPL,G:R,W Reference count 9 Default buffer size 512 WWID 01000010:6000-1FE1-0000-0D10-0009-8090-0677-0034 Total blocks 17769177 Sectors per track 169 Total cylinders 5258 Tracks per cylinder 20 Host name "WILD8" Host type, avail Compaq AlphaServer GS160 6/731, yes Alternate host name "W8GLX1" Alt. type, avail Compaq AlphaServer GS160 6/731, yes Allocation class 1 Volume label "S5SH_V72_SSS" Relative volume number 0 Cluster size 18 Transaction count 8 Free blocks 12812004 Maximum files allowed 467609 Extend quantity 5 Mount count 8 Mount status System Cache name "_$1$DGA8:XQPCACHE" Extent cache size 64 Maximum blocks in extent cache 1281200 File ID cache size 64 Blocks currently in extent cache 0 Quota cache size 0 Maximum buffers in FCP cache 1594 Volume owner UIC [1,1] Vol Prot S:RWCD,O:RWCD,G:RWCD,W:RWCD Volume Status: ODS-2, subject to mount verification, file high-water marking, write-back caching enabled. Volume is also mounted on H2OFRD, FIBRE3, NORLMN, SISKO, BOOLA, FLAM10, W8GLX1. I/O paths to device 5 Path PGA0.5000-1FE1-0000-0D12 (WILD8), primary path. Error count 2 Operations completed 130666 Path PGA0.5000-1FE1-0000-0D13 (WILD8), current path. Error count 1 Operations completed 30879310 Path PGA0.5000-1FE1-0000-0D11 (WILD8). Error count 0 Operations completed 130521 Path PGA0.5000-1FE1-0000-0D14 (WILD8). Error count 0 Operations completed 130539 Path MSCP (W8GLX1). Error count 0 Operations completed 1543163

For each path of the multipath device, the path identifier, the host name associated with that path, the path status, the error count, and the operations count are displayed.

The terms that may appear in the multiple paths portion of the display are described in Table 6-4.

Table 6-4 SHOW DEVICE/FULL Multipath Terms

Term	Description
WWID	The worldwide ID of the SCSI logical unit.
Host name	The name of the system that is being used by the current path. The host name is displayed if there is an MSCP path to a multipath device.
Alternate host name	The name of another system that can also provide access to the device. If the current path is a direct path, this will be the host currently associated with the MSCP path. If the current path is an MSCP path, this will be the name of the local system. The alternate host name is displayed if there is an MSCP path to a multipath disk device.
Primary path	This was the first path to the device found by the operating system.
Current path	This path is currently used for I/O.
User disabled	The DCL command SET DEVICE/NOENABLE has been executed for this path.
Polling disabled	The DCL command SET DEVICE/NOPOLL has been executed for this path.
Not responding	This path to the device was unusable the last time it was checked. Typically, the multipath poller checks every 60 seconds if the path is good and every 30 seconds if the path is bad.
Unavailable	The path is unavailable because the software driver has disconnected from the path.

6.7.5.2 Displaying Paths With SHOW DEVICE/MULTIPATH_SET

You can obtain a brief listing of multiple paths for a specific device, for all the devices in an allocation class, or for all devices with the DCL command:

SHOW DEVICE/MULTIPATH_SET [device-name]

The device name is optional; when omitted, all devices that have formed multipath sets are shown. For each multipath device found, the device name, host name, device status, error count, number of accessible paths, total number of paths, and the current path's path identifier are displayed.

The number of accessible paths can be less than the total number of paths for two reasons:

• A system manager disabled the path with the command SET DEVICE/PATH=pathname/NOENABLE.
• If a path is designated as Not Responding, the operating system decrements the total number of paths. This action was introduced in OpenVMS Alpha Version 7.3--1.

The host name displayed is the host name of the current path. For direct paths, this will be the local system's host name. For MSCP served paths, this will be the host name of the remote system which is serving access to the device.

The following example shows the output of a SHOW DEVICE/MULTIPATH command.

$ SHOW DEVICE/MULTIPATH Device Device Error Paths Current Name Status Count Avl/Tot path $1$DGA8: (H2OFRD) Mounted 3 5/ 5 PGA0.5000-1FE1-0000-0D12 $1$DGA10: (H2OFRD) ShadowSetMember 1 5/ 5 PGA0.5000-1FE1-0000-0D14 $1$DGA11: (WILD8) ShadowSetMember 3 3/ 3 MSCP $1$DGA23: (H2OFRD) Mounted 6 5/ 5 PGA0.5000-1FE1-0000-0D13 $1$DGA30: (H2OFRD) ShadowSetMember 8 5/ 5 PGA0.5000-1FE1-0000-0D13 $1$DGA31: (WILD8) ShadowMergeMbr 5 3/ 3 MSCP $1$DGA33: (H2OFRD) Online 0 5/ 5 PGA0.5000-1FE1-0000-0D12 $1$DGA40: (H2OFRD) Mounted 2 5/ 5 PGA0.5000-1FE1-0000-0D13 $1$DGA41: (H2OFRD) ShadowMergeMbr 8 5/ 5 PGA0.5000-1FE1-0000-0D12 $70$DKA100: (H2OFRD) Mounted 0 3/ 3 PKD0.1 $70$DKA104: (H2OFRD) ShadowSetMember 0 3/ 3 PKD0.1 $70$DKA200: (H2OFRD) ShadowSetMember 0 3/ 3 PKD0.2 $70$DKA300: (H2OFRD) ShadowSetMember 0 3/ 3 PKC0.3 $80$DKA1104: (H2OFRD) ShadowSetMember 0 3/ 3 PKD0.11 $80$DKA1200: (H2OFRD) ShadowSetMember 0 3/ 3 PKD0.12 $80$DKA1204: (H2OFRD) ShadowSetMember 0 3/ 3 PKC0.12 $80$DKA1207: (H2OFRD) Mounted 0 3/ 3 PKD0.12 $80$DKA1300: (H2OFRD) Mounted 0 3/ 3 PKD0.13 $80$DKA1307: (H2OFRD) ShadowSetMember 0 3/ 3 PKD0.13 $80$DKA1500: (H2OFRD) Mounted 0 3/ 3 PKD0.15 $80$DKA1502: (H2OFRD) ShadowSetMember 0 3/ 3 PKD0.15

If you choose to specify a partial device name, such as $70$DKA, the display shows all devices with multiple paths whose names begin with $70$DKA.