Cluster File System Architecture
About Veritas Cluster Volume Manager Functionality
The following table summarizes the allowed and conflicting activation modes for shared disk groups:
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| Allowed and conflicting activation modes |
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| Disk group | Attempt to activate disk group on another node as: | ||||
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| activated in | exclusive- | readonly |
| sharedread | sharedwrite |
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| cluster as: |
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| write |
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| exclusivewrite | Fails | Fails |
| Succeeds | Fails |
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| readonly | Fails | Succeeds |
| Succeeds | Fails |
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| sharedread | Succeeds | Succeeds |
| Succeeds | Succeeds |
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| sharedwrite | Fails | Fails |
| Succeeds | Succeeds |
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| Shared disk groups can be automatically activated in any mode during disk group | |||||
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| creation or during manual or | |||||
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| groups, the defaults file /etc/default/vxdg must be created. |
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| The defaults file /etc/default/vxdg must contain the following lines: | |||||
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| enable_activation=true |
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| The | |||||
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| off. |
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| When a shared disk group is created or imported, it is activated in the specified mode. | |||||
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| When a node joins the cluster, all shared disk groups accessible from the node are | |||||
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| activated in the specified mode. |
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NOTE |
| The activation mode of a disk group controls volume I/O from different nodes in the | |||||
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| cluster. It is not possible to activate a disk group on a given node if it is activated in a | |||||
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| conflicting mode on another node in the cluster. When enabling activation using the | |||||
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| defaults file, it is recommended that this file be made identical on all nodes in the | |||||
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| cluster. Otherwise, the results of activation are unpredictable. |
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| If the defaults file is edited while the vxconfigd daemon is already running, the | |||||
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| vxconfigd process must be restarted for the changes in the defaults file to take effect. | |||||
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| If the default activation mode is anything other than off, an activation following a cluster | |||||
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| join, or a disk group creation or import can fail if another node in the cluster has | |||||
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| activated the disk group in a conflicting mode. |
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| To display the activation mode for a shared disk group, use the vxdg list diskgroup | |||||
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| command. |
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| You can also use the vxdg command to change the activation mode on a shared disk | |||||
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| group. |
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Connectivity Policy of Shared Disk Groups
The nodes in a cluster must always agree on the status of a disk. In particular, if one node cannot write to a given disk, all nodes must stop accessing that disk before the results of the write operation are returned to the caller. Therefore, if a node cannot
24 | Chapter 2 |
