Dell PowerVault MD 32XX/36XX Series Storage Arrays CLI Guide

Create Snapshot Group

Description

This command creates a new snapshot group and the associated repository virtual disk. A snapshot group contains a sequence of snapshot images of an associated base virtual disk. A snapshot group has a repository virtual disk that is used to save data for all of the snapshot images that are part of the snapshot group.

Syntax

create snapGroup userLabel="snapGroupName" sourceVirtualDisk="virtualDiskName" [(repositoryVirtualDisk="repos_xxxx" | repositoryVirtualDisk=(diskGroupName
                                 [capacity=capacityValue]) | repositoryVirtualDisk=(diskPoolName [capacity=capacityValue]))] [repositoryFullPolicy=(failBaseWrites
                                 | purgeSnapImages)] [rollbackPriority=(highest | high | medium | low | lowest)] [repositoryFullLimit=percentValue] [autoDeleteLimit=numberOfSnapImages]|
                                 [enableSchedule=(TRUE | FALSE)] [schedule (immediate | snapshotSchedule)]

Parameters

Parameter	Description
`userLabel`	The alphanumeric identifier (including - and _) that you want to give the new snapshot group. Enclose the snapshot group identifier in double quotation marks (" ").
`sourceVirtualDisk`	The alphanumeric identifier (including - and _) of the virtual disk that you want to use as the source for your snapshot images. Enclose the source virtual disk name in double quotation marks (" ").
`repositoryVirtualDisk`	The name of the repository virtual disk that contains the snapshot group. Enclose the snapshot repository virtual disk name in double quotation marks (" "). The repository virtual disk name is comprised of two parts: The term `repos` A four-digit numerical identifier that you assign to the repository virtual disk name
`repositoryFullPolicy`	Defines how snapshot image processing continues if the snapshot image repository virtual disk is full. You can choose to fail writes to the base virtual disk ( `failBaseWrites`) or delete (purge) the snapshot images ( `purgeSnapImages`). The default action is `purgeSnapImages`.
`rollBackPriority`	Determines whether system resources should be allocated to the rollback operation at the expense of system performance. A value of `high` indicates that the rollback operation is prioritized over all other host I/O. A value of `low` indicates that the rollback operation should be performed with minimal impact to host I/O. The default value is `medium`.
`repositoryFullLimit`	The percentage of repository capacity at which you receive a warning that the snapshot image repository virtual disk is nearing full. Use integer values. For example, a value of `70` means 70 percent. The default value is `75`.
`autoDeleteLimit`	The maximum number of snapshot images that you want to automatically delete if you have selected to purge the snapshot images for the repository full policy. The default value is `32`.

Notes

Each snapshot group user label must be unique. You can use any combination of alphanumeric characters, underscore (_), hyphen(-), and pound (#) for the user label. User labels can have a maximum of 30 characters.

To create a snapshot group, you must have an associated repository virtual disk in which you store the snapshot images. You can either use an existing repository virtual disk or create a new repository virtual disk. You can create the repository virtual disk when you create the snapshot group. A snapshot group repository virtual disk is an expandable virtual disk that is structured as a concatenated collection of up to 16 standard virtual disk entities. Initially, an expandable repository virtual disk has only a single element. The capacity of the expandable repository virtual disk is exactly that of the single element. You can increase the capacity of an expandable repository virtual disk by attaching additional standard virtual disks to it. The composite expandable repository virtual disk capacity then becomes the sum of the capacities of all of the concatenated standard virtual disks.

A snapshot group has a strict ordering of snapshot images based on the time that each snapshot image is created. A snapshot image that is created after another snapshot image is a successor relative to that other snapshot image. A snapshot image that is created before another snapshot image is a predecessor relative to that other one.

A snapshot group repository virtual disk must satisfy a minimum capacity requirement that is the sum of the following:

32 MB to support fixed overhead for the snapshot group and for copy-on-write processing.
Capacity for rollback processing, which is 1/5000th of the capacity of the base virtual disk.

The minimum capacity is enforcement by the RAID controller module firmware and the MD storage management software.

When a you first create a snapshot group, it does not contains any snapshot images. When you create snapshot images, you add the snapshot images to a snapshot group. Use the create snapImage command to create snapshot images and add the snapshot images to a snapshot group.

A snapshot group can have one of these states:

Optimal	The snapshot group is operating normally.
Full	The snapshot group repository is full. Additional copy-on-write operations can not be performed. This state is possible only for snapshot groups that have the Repository Full policy set to Fail Base Writes. Any snapshot group in a Full state causes a Needs-Attention condition to be posted for the storage array.
Over Threshold	The snapshot group repository virtual disk usage is at or beyond its alert threshold. Any snapshot group in this state causes a Needs-Attention condition to be posted for the storage array.
Failed	The snapshot group has encountered a problem that has made all snapshot images in the snapshot group unusable. For example, certain types of repository virtual disk failures can cause a Failed state. To recover from a Failed state use the `revive snapGroup` command.

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