Dell PowerVault MD3420 - Manual (Page 189)

Parameter Description
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.
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