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How to use EMC PowerPaht multipath software

First, introduce the function of multipath software:

Ordinary computer mainframe is a hard disk attached to a bus, here is an one-to-one relationship. When it comes to the SAN environment composed of optical fiber, because the host and storage are connected through the optical fiber switch, this constitutes a many-to-many relationship. That is, there can be multiple paths from the host to the storage.

Each host can go through several different paths to the corresponding storage. If it is used at the same time, how is the Icano traffic allocated? One of the paths is broken, how to deal with it? And from the operating system's point of view, each path will be regarded as an actual physical disk, but in fact it is only a different path to the same physical disk, which brings confusion to the user when using it. Multipath software came into being to solve the above problems. The main function of multipathing is to work with storage devices to achieve the following functions:

Failure switching and recovery

Load balancing of IO traffic

Virtualization of disk

Multipathing software needs to be used with storage, such as EMC VNX 5600 storage and its multipathing software EMC PowerPath.

Second, EMCPowerPath common commands

| | powermt check | check the PowerPath channel manually |

| | powermt restore | restore the PowerPath tunnel manually |

| | powermt save | Save the device database file of EMC PowerPath |

| | powermt watch | Monitoring PowerPath tunnel |

| | powermt config | identify PowerPath device |

| | powermt display | displays the HBA status configured by powerpath. Common commands are: powermt display dev=all |

| | powermt load | load a previously saved powerpath configuration |

| | powermt remove | Delete a path in the powerpath configuration |

| | powermt version | displays the version of powerpath installed on the server |

III. Modification of equipment number

When working on a cluster (or HA) system, the same LUN will be allocated to two or more servers at the same time. At this time, after the allocation of multiple LUN is completed, it will be found that the device numbers seen by the same LUN on multiple servers are not the same, which is unacceptable to the application.

For example: ServerA,ServerB,ServerC, there are three LUN assigned to these three servers at the same time, namely LUN0,LUN1,LUN2, the assignment is completed, and the HBA driver is restarted. After PowerPath, the corresponding device number is as follows:

| | Lun ID | ServerA | ServerB | ServerC | |

|-- |

| | LUN0 | / dev/emcpowera | / dev/emcpowerb | / dev/emcpowerc | |

| | LUN1 | / dev/emcpowerb | / dev/emcpowerc | / dev/emcpowera | |

| | LUN2 | / dev/emcpowerc | / dev/emcpowera | / dev/emcpowerb | |

Method 1: manually modify the device number

Here, based on the device number on ServerA, the device number of ServerB and ServerC is changed to be the same as ServerA.

Enter emcpadm on ServerB to get detailed command help, as follows:

Emcpadm renamepseudo-s / dev/emcpowerb-t / dev/emcpowerzemcpadm renamepseudo-s / dev/emcpowerc-t / dev/emcpowerbemcpadm renamepseudo-s / dev/emcpowera-t / dev/emcpowercemcpadm renamepseudo-s / dev/emcpowerz-t / dev/emcpowera

Change the device number in the same way as 2 in ServerC

After completion, reboot all three servers once, and after startup, reconfirm whether the device numbers on the three servers are the same.

Method 2: synchronize configuration files

Or you can export the configuration file of ServerA, and then import it to another machine, and export the command:

Emcpadm export_mappings-f powerpath.cc

Note: powerpath.cc is the specified exported file name, which can be customized. Use the scp command to transfer the powerpath.cc file to another server.

Import commands:

Emcpadm import_mappings-f powerpath.cc

Then restart the server.

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