Administrator Guide

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 enables you to limit the automatic growth of a virtual disk
to an amount less than the defined virtual capacity.
NOTE: Because less than full capacity is allocated when you create a thin virtual disk, insufficient free capacity may
exist when certain operations are performed, such as snapshot images and snapshot virtual disks. If this occurs, an alert
threshold warning is displayed.
Thin virtual disk requirements and limitations
The following table provides the minimum and maximum capacity requirements applicable to thin virtual disks.
Table 8. Minimum and maximum capacity requirements
Capacity Types Size
Virtual capacity
Minimum 32 MB
Maximum 63 TB
Physical capacity
Minimum 4 GB
Maximum 64 TB
The following limitations apply to thin virtual disks:
• The segment size of a thin virtual disk cannot be changed.
• The pre-read consistency check for a thin virtual disk cannot be enabled.
• A thin virtual disk cannot serve as the target virtual disk in a Virtual Disk Copy.
• A thin virtual disk cannot be used in a Remote Replication (Legacy) operation.
Thin virtual disk attributes
When you create a thin virtual disk from free capacity in an existing disk pool, you can manually set disk attributes or allow MD Storage
Manager to assign default attributes. The following manual attributes are available:
• Preferred Capacity — Sets the initial physical capacity of the virtual disk (MB, GB or TB). Preferred capacity in a disk pool is
allocated in 4 GB increments. If you specify a capacity amount that is not a multiple of 4 GB, MD Storage Manager assigns a 4 GB
multiple and assigns the remainder as unused. If space exists that is not a 4 GB multiple, you can use it to increase the size of the thin
virtual disk. To increase the size of the thin virtual disk, select Storage > Virtual Disk > Increase Capacity.
• Repository Expansion Policy — Select either Automatic or Manual to indicate whether MD Storage Manager must automatically
expand physical capacity thresholds. If you select Automatic, enter a Maximum Expansion Capacity value that triggers automatic
capacity expansion. The MD Storage Manager expands the preferred capacity in increments of 4 GB until it reaches the specified
capacity. If you select Manual, automatic expansion does not occur and an alert is displayed when the Warning Threshold value
percentage is reached.
• Warning Threshold — When consumed capacity reaches the specified percentage, MD Storage Manager sends an E-mail or SNMP
alert.
Thin virtual disk states
The following are the virtual disk states displayed in MD Storage Manager:
• Optimal — Virtual disk is operating normally.
• Full — Physical capacity of a thin virtual disk is full and no more host write requests can be processed.
Disk groups, standard virtual disks, and thin virtual disks
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