A mirrored volume provides data redundancy by containing more than one copy of its data. Each copy (or mirror) is stored on different disks from the original copy of the volume and from other mirrors. Mirroring a volume ensures that its data is not lost if a disk in one of its component mirrors fails.
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 | NOTE: A mirrored volume requires space to be available on at least as many disks in the disk group as the number of mirrors in the volume. |
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To create a new mirrored volume, use the following command:
# vxassist [-g diskgroup] make volume length layout=mirror \
[nmirror=number] |
For example, to create the mirrored volume, volmir, use the following command:
# vxassist make volmir 5g layout=mirror |
To create a volume with 3 instead of the default of 2 mirrors, modify the command to read:
# vxassist make volmir 5g layout=mirror nmirror=3 |
Creating a Mirrored-Concatenated Volume |
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A mirrored-concatenated volume mirrors several concatenated plexes. To create a concatenated-mirror volume, use the following command:
# vxassist [-g diskgroup] make volume length layout=mirror-concat \
[nmirror=number] |
Alternatively, first create a concatenated volume, and then mirror it as described in “Adding a Mirror to a Volume”.
Creating a Volume with a DCO and DCO Log Volume |
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If a data change object (DCO) and DCO volume are attached to a volume, this allows Persistent FastResync to be used with the volume. (See “How Persistent FastResync Works with Snapshots” for details of how Persistent FastResync performs fast resynchronization of snapshot mirrors when they are returned to their original volume.)
To perform fast resynchronization of mirrors after a system crash or reboot, you must also enable dirty region logging (DRL) on a mirrored volume. To add a DCO object and DCO log volume to a volume on which DRL logging is enabled, follow the procedure described in “Adding a DCO and DCO Log Volume”.
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| NOTE: You may need an additional license to use the Persistent FastResync feature. Even if you do not have a license, you can configure a DCO object and DCO log volume so that snap objects are associated with the original and snapshot volumes. For more information about snap objects, see
“How Persistent FastResync Works with Snapshots”. |
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Dirty region logging (DRL) is the default log type if you specify the log attribute to enable logging on a mirrored volume, but do not use the logtype attribute to specify the type of logging to vxassist.
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| NOTE: Only one type of logging may initially be specified when you use vxassist to create a volume. |
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To create a volume with an attached DCO object and DCO log volume, use the following procedure:
Ensure that the disk group has been upgraded to at least version 90. Use the following command to check the version of a disk group:
To upgrade a disk group to the latest version, use the following command:
For more information, see “Upgrading a Disk Group”.
Use the following command to create the volume (you may need to specify additional attributes to create a volume with the desired characteristics):
#
vxassist [-g diskgroup] make volume length layout=layout \
logtype=dco [ndcolog=number] [dcologlen=size] [fastresync=on] |
The default number of plexes in the mirrored DCO log volume is 2 unless you use the ndcolog attribute to specify a different number. It is recommended that you configure as many DCO plexes as there are data plexes in the volume. For example, specify ndcolog=3 when creating a 3-way mirrored volume.
The default size of each plex is 132 blocks unless you use the dcologlen attribute to specify a different size. If specified, the size of the plex must be a multiple of 33 blocks from 33 up to a maximum of 2112 blocks.
By default, FastResync is not enabled on newly created volumes. Specify the fastresync=on attribute if you want to also enable FastResync on the volume. If a DCO object and DCO log volume are associated with the volume, Persistent FastResync is enabled; otherwise, Non-Persistent FastResync is enabled.
For more information about configuring DCO, see the vxassist(1M) manual page.
Creating a Mirrored Volume with DRL Logging Enabled |
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To create a mirrored volume with dirty region logging (DRL) enabled, use this command:
# vxassist [-g diskgroup] make volume length layout=mirror \
logtype=drl |
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| NOTE: By default, the vxassist command creates one log plex for a mirrored volume. |
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For a volume that will be written to sequentially, such as a database log volume, use the following command to specify that sequential DRL is to be used:
# vxassist [-g diskgroup] make volume length layout=mirror \
logtype=drlseq |
To add DRL logging to a volume that has DCO enabled, or to change the number of DRL logs, follow the procedure that is described in “Adding DRL Logging to a Mirrored Volume”.
If you use ordered allocation when creating a mirrored volume on specified storage, you can use the optional logdisk attribute to specify on which disks the log plexes should be created. Use the following form of the vxassist command to specify the disks from which space for the logs is to be allocated:
# vxassist [-g diskgroup] -o ordered make volume length \
layout=mirror logtype=log_type logdisk=disk[,disk,...] \
storage_attributes |
If you do not specify the logdisk attribute, vxassist locates the logs in the data plexes of the volume.
For more information about ordered allocation, see “Specifying Ordered Allocation of Storage to Volumes”
and the vxassist(1M) manual page.
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