This chapter describes how the Virtual Disk Copy feature works, lists the script commands for Virtual Disk Copy, and explains how to use the commands to create and run Virtual Disk Copy. Additional information about Virtual Disk Copy and related definitions is available in the online help, the Installation Guide, the MD Storage Manager User's Guide, and the Owner's Manual.
NOTE: If you ordered Premium Features for Virtual Disk Copy, you received a Premium Features Activation card shipped in the same box as your Dell PowerVault™ MD storage array. Follow the directions on the card to obtain a key file and to enable the feature. For more information, see "Premium Feature — Virtual Disk Copy" in the User's Guide.
The Virtual Disk Copy feature enables you to copy data from one virtual disk (the source) to another virtual disk (the target) in a single storage array. You can use this feature to perform the following functions:
Back up data.
Copy data from disk groups that use smaller capacity physical disks to disk groups using larger capacity physical disks.
Restore snapshot virtual disk data to the associated source virtual disk.
NOTE: The preferred method is to perform a Virtual Disk Copy from a Snapshot Virtual Disk. This allows the original virtual disk used in the Snapshot operation to remain in full use while the Snapshot of this virtual disk is used as the source for the virtual disk copy operation.
NOTE: The Virtual Disk Copy for any Virtual Disk cannot be mounted on the same host as the source Virtual Disk. The Microsoft® Windows® operating system does not allow assigning a drive letter to the Virtual Disk Copy.
Table 5-1 lists the Virtual Disk Copy commands and briefly describes what the commands do.
Table 5-1. Virtual Disk Copy Commands
Command
Description
create virtualDiskCopy
Creates a virtual disk copy and starts the virtual disk copy operation.
disable storageArray feature=virtualDiskCopy
Turns off the current virtual disk copy operation.
enable storageArray feature
Activates the Virtual Disk Copy feature.
recopy virtualDiskCopy
Re-initiates a virtual disk copy operation by using an existing virtual disk copy pair.
remove virtualDiskCopy
Removes a virtual disk copy pair.
set virtualDiskCopy
Defines the properties for a virtual disk copy pair.
show virtualDiskCopy
Returns information about virtual disk copy operations. You can retrieve information about a specific virtual disk copy pair, or all virtual disk copy pairs in the storage array.
show virtualDiskCopy sourceCandidates
Returns information about the candidate virtual disks that you can use as the source for a virtual disk copy operation.
show virtualDiskCopy targetCandidates
Returns information about the candidate virtual disks that you can use as the target for a virtual disk copy operation.
stop virtualDiskCopy
Stops a virtual disk copy operation.
Creating a Virtual Disk Copy
Before creating a virtual disk copy, ensure that a suitable target virtual disk exists on the storage array, or create a new target virtual disk specifically for the virtual disk copy. The target virtual disk must have a capacity equal to or greater than the source virtual disk.
You can have a maximum of eight virtual disk copies in progress at one time. Any virtual disk copy greater than eight has a status of Pending until one of the virtual disk copies with a status of In Progress completes.
The following steps show the general process for creating a virtual disk copy:
Enable the Virtual Disk Copy feature.
Determine candidates for a virtual disk copy.
Create the target virtual disk and source virtual disk for a virtual disk copy.
Enabling the Virtual Disk Copy Feature
The first step in creating a virtual disk copy is to make sure the feature is enabled on the storage array. You need a feature key to enable the feature. To enable the feature key file, use the command:
enable storageArray feature file="filename"
where the file parameter is the complete file path and file name of a valid feature key file. Enclose the file path and file name in quotation marks (" "). Valid file names for feature key files usually end with a .key extension.
Determining Virtual Disk Copy Candidates
All virtual disks might not be available for use in virtual disk copy operations. To determine which candidate virtual disks on the storage array can be used as a source virtual disk, use theshow virtualDiskCopy sourceCandidatescommand. To determine which candidate virtual disks on the storage array can be used as a target virtual disk, use the show virtualDiskCopy targetCandidates command. These commands return a list of the expansion enclosure, slot, and capacity information for source virtual disk and target virtual disk candidates. You can use the show virtualDiskCopy sourceCandidates and the show virtualDiskCopy targetCandidates commands only after you have enabled the virtual disk copy feature.
Creating a Virtual Disk Copy
NOTICE: A virtual disk copy overwrites data on the target virtual disk. Ensure that you no longer need the data or have backed up the data on the target virtual disk before starting a virtual disk copy.
When you create a virtual disk copy, you must define which virtual disks to use for the source virtual disk and target virtual disks. Define the source virtual disk and target virtual disk by the name of each virtual disk. You can also define the copy priority and choose whether you want the target virtual disk to be write enabled or read only after the data is copied from the source virtual disk.
Preparing Host Servers to Create a Virtual Disk Copy
NOTICE: Before you create a new copy of a source virtual disk, stop any data access (I/O) activity or suspend data transfer to the source virtual disk (and, if applicable, the target disk) to ensure that you capture an accurate point-in-time image of the source virtual disk. Close all applications, including Windows Internet Explorer, to make sure all I/O activity has stopped.
NOTE: Removing the drive letter of the associated virtual disk(s) in Windows or unmounting the virtual drive in Linux will help to guarantee a stable copy of the drive for the virtual disk copy.
Before creating a virtual disk copy, both the server and the associated virtual disk you are copying have to be in the proper state. To ensure that the host server is properly prepared to create a virtual disk copy, you can either use an application to carry out this task, or you can perform the following steps:
Stop all I/O activity to the source and target virtual disk.
Using your Windows system, flush the cache to both the source and the
target virtual disk (if mounted). At the host prompt, type
SMrepassist -f <filename-identifier>
and press <Enter>. See "SMrepassist Utility" in the User's Guide for more information.
Remove the drive letter(s) of the source and (if mounted) virtual disk in
Windows or unmount the virtual drive(s) in Linux to help guarantee a
stable copy of the drive for the virtual disk. If this is not done, the copy
operation will report that it has completed successfully, but the copied
data will not be updated properly.
Follow any additional instructions for your operating system. Failure to
follow these additional instructions can create unusable virtual disk copies.
NOTE: If your operating system requires additional instructions, you can find those instructions in your operating system documentation.
After first preparing the host server(s) as specified in the preceding procedure, use the following examples to make a virtual disk copy.
The following syntax is the general form of the command:
create virtualDiskCopy source="sourceName" target="targetName" [copyPriority=(highest | high | medium | low | lowest) targetReadOnlyEnabled=(TRUE | FALSE)]
NOTE: Use one or both of the optional parameters as needed to help define your configuration. It is not necessary to use any optional parameters.
Once the virtual disk copy has started, the source virtual disk will be read only to all I/O activity. Any write attempts to the source virtual disk will fail until the operation completes.
Once the virtual disk copy operation is completed register the target virtual disk with the OS to be used by performing the following steps:
Enable write permission on the target virtual disk by either removing the Virtual Disk Copy Pair or explicitly setting write permission.
In Windows, assign a drive letter to the virtual disk.
The command in this example copies the data from the source virtual disk named Jaba_Hut to the target virtual disk named Obi_1. Setting the copy priority to medium provides a compromise between the following storage array operations:
The speed with which the data is copied from the source virtual disk to the target virtual disk
The amount of processing resource required for data transfers to other virtual disks in the storage array
Setting thetargetReadOnlyEnabledparameter to TRUE means that write requests cannot be made to the target virtual disk. This setting also ensures that the data on the target virtual disk remains unaltered.
After the virtual disk copy operation is completed, the target virtual disk automatically becomes read-only to the hosts. Any write requests to the target virtual disk are rejected, unless you disable the read-only attribute. Use the set virtualDiskCopy command to disable the read-only attribute.
Viewing Virtual Disk Copy Properties
Using the show virtualDiskCopy command, you can view information about one or more selected source virtual disks or target virtual disks. This command returns the following information:
The virtual disk role (target or source)
The copy status
The start timestamp
The completion timestamp
The virtual disk copy priority
The read-only attribute setting for the target virtual disk
The source virtual disk World Wide Identifier (WWID) or the target virtual disk WWID
A virtual disk can be a source virtual disk for one virtual disk copy and a target virtual disk for another virtual disk copy. If a virtual disk participates in more than one virtual disk copy, the details are repeated for each associated copy pair.
The following syntax is the general form of the command:
show virtualDiskCopy (allVirtualDisks | source [sourceName] | target [targetName])
The following example shows a command that returns information about a virtual disk used for a virtual disk copy:
The command in the preceding example requests information about the source virtual disk Jaba_Hut. If you want information about all virtual disks, use the allVirtualDisksparameter. You can also request information about a specific target virtual disk.
The following example is the script file version of the command:
show virtualDiskCopy source ["Jaba_Hut"];
Changing Virtual Disk Copy Settings
The set virtualDiskCopy command enables you to change the property settings for a virtual disk copy pair. Using this command, you can change the following items:
Copy priority
Read/write permission for the target virtual disk
Copy priority has five relative settings, which range from highest to lowest. The highest priority supports the virtual disk copy, but I/O activity might be affected. The lowest priority supports I/O activity, but the virtual disk copy takes longer. You can change the copy priority at three different times in the operation:
Before the virtual disk copy begins
While the virtual disk copy has a status of In Progress
After the virtual disk copy has completed re-creating a virtual disk copy using the recopy virtualDiskCopy command
When you create a virtual disk copy pair and after the original virtual disk copy has completed, the target virtual disk is automatically defined as read-only to the hosts. The read-only status of the target virtual disk ensures that the copied data on the target virtual disk is not corrupted by additional writes to the target virtual disk after the virtual disk copy is created. Maintain the read-only status when the following conditions apply:
You are using the target virtual disk for backup purposes
You are copying data from one disk group to a larger disk group for greater accessibility
You are planning to use the data on the target virtual disk to copy back to the source virtual disk in case of a disabled or failed snapshot virtual disk
At other times you might want to write additional data to the target virtual disk. You can use the set virtualDiskCopy command to reset the read/write permission for the target virtual disk.
NOTE: If you enabled host writes to the target virtual disk, read and write requests are rejected while the virtual disk copy has a status of In Progress, Pending, or Failed.
The following syntax is the general form of the command:
set virtualDiskCopy target [targetName] [source [sourceName]] copyPriority=(highest | high | medium | low | lowest) targetReadOnlyEnabled=(TRUE | FALSE)
NOTE: Use one or both of the parameters as needed to help define your configuration. It is not necessary to use either parameter.
The following example shows how to change parameters using the set virtualDiskCopy command:
The following example is the script file version of the command:
set virtualDiskcopy target ["Obi_1"] copyPriority=highest targetreadonlyenabled=false;
Recopying a Virtual Disk
NOTICE: The recopy virtualDiskCopy command overwrites existing data on the target virtual disk and makes the target virtual disk read-only to hosts. The recopy virtualDiskCopy command fails all snapshot virtual disks associated with the target virtual disk, if any exist.
Using the recopy virtualDiskCopy command, you can create a new virtual disk copy for a previously defined copy pair that has a status of Stopped, Failed, or Completed. Use the recopy virtualDiskCopy command to create backups of the target virtual disk, then copy the backup to tape for off-site storage. When using the recopy virtualDiskCopy command to make a backup, you cannot write to source while the recopy is running. The recopy might take a long time.
When you run the recopy virtualDiskCopy command, the data on the source virtual disk is copied in its entirety to the target virtual disk.
Reset the copy priority for the recopy operation by using the recopy virtualDiskCopy command. The higher priorities allocate storage array resources to the virtual disk copy at the expense of storage array performance.
Preparing Host Servers to Recopy a Virtual Disk
NOTICE: Before you create a new copy of a source virtual disk, stop any data access (I/O) activity or suspend data transfer to the source virtual disk (and, if applicable, the target disk) to ensure that you capture an accurate point-in-time image of the source virtual disk. Close all applications, including Windows Internet Explorer, to make sure all I/O activity has stopped.
NOTE: Removing the drive letter of the associated virtual disk(s) in Windows or unmounting the virtual drive in Linux will help to guarantee a stable copy of the drive for the virtual disk copy.
Before creating a new virtual disk copy for an existing copy pair, both the server and the associated virtual disk you are recopying have to be in the proper state. To ensure that the host server is properly prepared to create a virtual disk recopy, you can either use an application to carry out this task, or you can perform the following steps:
Stop all I/O activity to the source and target virtual disk.
Using your Windows system, flush the cache to both the source and the
target virtual disk (if mounted). At the host prompt, type
SMrepassist -f <filename-identifier>
and press <Enter>. See "SMrepassist Utility" in the User's Guide for more information.
Remove the drive letter(s) of the source and (if mounted) virtual disk in
Windows or unmount the virtual drive(s) in Linux to help guarantee a
stable copy of the drive for the virtual disk. If this is not done, the copy
operation will report that it has completed successfully, but the copied
data will not be updated properly.
Follow any additional instructions for your operating system. Failure to
follow these additional instructions can create unusable virtual disk copies.
NOTE: If your operating system requires additional instructions, you can find those instructions in your operating system documentation.
The command in this example copies data from the source virtual disk associated with the target virtual disk Obi_1 to the target virtual disk again. The copy priority is set to the highest value to complete the virtual disk copy as quickly as possible. The underlying consideration for using this command is that you have already created the virtual disk copy pair. When you create a virtual disk copy pair, you automatically created one virtual disk copy. Using this command, you are copying the data from the source virtual disk to the target virtual disk. You are making this copy because the data on the source virtual disk changed since the previous copy was made.
The stop virtualDiskCopy command enables you to stop a virtual disk copy that has a status of In Progress, Pending, or Failed. After you stop a virtual disk copy, you can use the recopy virtualDiskCopy command to create a new virtual disk copy using the original virtual disk copy pair. All mapped hosts will have write access to the source virtual disk.
The following syntax is the general form of the command:
The following example is the script file version of the command:
stop virtualDiskCopy target ["Obi_1"];
Removing Copy Pairs
The remove virtualDiskCopy command enables you to remove a virtual disk copy pair from the storage array configuration. All virtual disk copy information for the source virtual disk and target virtual disk is removed from the storage array configuration. The data on the source virtual disk or target virtual disk is not deleted. Removing a virtual disk copy from the storage array configuration also removes the read-only attribute for the target virtual disk.
NOTICE: If the virtual disk copy has a status of In Progress, you must stop the virtual disk copy before you can remove the virtual disk copy pair from the storage array configuration.
The following syntax is the general form of the command:
The following example is the script file version of the command:
remove virtualDiskCopy target ["Obi_1"];
Interaction with Other Features
You can run the Virtual Disk Copy feature while running the following features:
Storage Partitioning
Snapshot Virtual Disks
When running the Virtual Disk Copy feature with other features, you must take the requirements of other features into consideration to ensure you set up a stable storage array configuration.
You can also run the Virtual Disk Copy feature while running Dynamic Virtual Disk Expansion.
Storage Partitioning
Storage partitioning enables hosts to share access to virtual disks in a storage array. You create a storage partition when you define the following storage array assignments:
A host
A host group
Virtual disk-to-logical unit number (LUN) mapping
The virtual disk-to-LUN mapping enables you to define which host group or host has access to a particular virtual disk in the storage array.
After you create a virtual disk copy, the target virtual disk automatically becomes read-only to hosts to ensure that the data is preserved. Hosts that have been mapped to a target virtual disk do not have write access to the virtual disk, and any attempt to write to the read-only target virtual disk results in a host I/O error.
If you want hosts to have write access to the data on the target virtual disk, use the set virtualDiskCopy command to disable the read-only attribute for the target virtual disk.
Snapshot Virtual Disks
A snapshot virtual disk is a point-in-time image of a virtual disk. It is typically created so that an application, such as a backup, can access the snapshot virtual disk and read the data while the source virtual disk remains online and accessible to hosts.
NOTICE: Before using the source virtual disk of a snapshot virtual disk as your target, you must disable all snapshot virtual disks associated with the source virtual disk. By disabling the snapshot virtual disks, you avoid altering the snapshot data if the source virtual disk is changed.
Creating a snapshot virtual disk automatically creates a snapshot repository virtual disk. The snapshot repository virtual disk stores information about the data that has changed since the snapshot virtual disk was created. Snapshot repository virtual disks cannot be selected as a source virtual disk or target virtual disk in a virtual disk copy.
The virtual disk for which the point-in-time image is created is the source virtual disk and must be a standard virtual disk in the storage array.
You can select snapshot virtual disks as the source virtual disk for a virtual disk copy. Selecting a snapshot virtual disk is a good use of this feature, because it enables complete backups without significant impact to the storage array I/O. However, some I/O processing resources are lost to the copy operation.
The Snapshot Virtual Disk feature can be used with the Virtual Disk Copy feature to back up data on the same storage array and to restore the data on the snapshot virtual disk back to its original source virtual disk.
