Dell PowerVault MD3820f - Manual (Page 86)

6. In the confirmation dialog, click Yes.
A progress dialog is displayed, which indicates the number of virtual disks being changed.
Thin Virtual Disks
When creating virtual disks from a disk pool, you have the option to create thin virtual disks instead of
standard virtual disks. Thin virtual disks are created with physical (or preferred) and virtual capacity,
allowing flexibility to meet increasing capacity requirements.
When you create standard virtual disks, you allocate all available storage based on an estimation of how
much space you need for application data and performance. If you want to expand the size of a standard
virtual disk in the future, you must add physical disks to your existing disk groups or disk pools. Thin
volumes allow you to create large virtual disks with smaller physical storage allocations that can be
increased as required.
NOTE: Thin virtual disks can only be created from an existing disk pool.
Advantages Of Thin Virtual Disks
Thin virtual disks, also known as thin provisioning, present a more logical storage view to hosts.
Thin virtual disks allow you to dynamically allocate storage to each virtual disk as data is written. Using
thin provisioning helps to eliminate large amounts of unused physical capacity that often occurs when
creating standard virtual disks.
However, in certain cases, standard virtual disks may provide a more suitable alternative compared to thin
provisioning, such as in situations when:
• you anticipate that storage consumption on a virtual disk is highly unpredictable or volatile
• an application relying on a specific virtual disk is exceptionally mission critical
Physical Vs Virtual Capacity On A Thin Virtual Disk
When you configure a thin virtual disk, you can specify the following types of capacity:
• physical (or preferred)
• virtual
Virtual capacity is capacity that is reported to the host, while physical capacity is the amount of actual
physical disk space allocated for data write operations. Generally, physical capacity is much smaller than
virtual capacity.
Thin provisioning allows virtual disks to be created with a large virtual capacity but a relatively small
physical capacity. This is beneficial for storage utilization and efficiency because it allows you to increase
capacity as application needs change, without disrupting data throughput. You can also set a utilization
warning threshold that causes MD Storage Manager to generate an alert when a specified percentage of
physical capacity is reached.
Changing Capacity On Existing Thin Virtual Disks
If the amount of space used by the host for read/write operations (sometimes called consumed capacity)
exceeds the amount of physical capacity allocated on a standard virtual disk, the storage array cannot
accommodate additional write requests until the physical capacity is increased. However, on a thin virtual
disk, MD Storage Manager can automatically expand physical capacity of a thin virtual disk. You can also
do it manually using Storage → Virtual Disk → Increase Repository Capacity. If you select the automatic
expansion option, you can also set a maximum expansion capacity. The maximum expansion capacity
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