space allocated does not need to be contiguous. In the event that the allocated capacity reaches the physical disk capacity, the write operation fails.
Thin provisioned virtual disks differ from standard virtual disks as follows:
Thin provisioned disk | Standard virtual disk |
The amount of physical disk space allocated can automatically change in response to the amount of data being stored, up to the specified size of the virtual disk or until all available disk space is used
Requires the full amount of physical disk space to be allocated at all times
Does not require explicit resizing (manually or with scripts)
Has no unused physical disk space
The maximum requested capacity can exceed the amount of available physical disk capacity that can be allocated
Must be explicitly resized whenever the amount of disk space needs to be changed
Physical disk space that is allocated but unused can create stranded capacity
The requested capacity is limited by the amount of available physical disk capacity that can be allocated
The following example demonstrates thin provisioning:
A storage administrator is planning to create two virtual disks for two new host applications. His HP P6000 storage system currently has a total capacity of 10 TB, with 6 TB unused disk space. The administrator determines that each host application initially requires 2 TB of disk space, but eventually, the host applications will require 4 TB of space. With these requirements in mind, the administrator creates two 4 TB thin provisioned virtual disks.
Each host application recognizes a 4 TB virtual disk, even though initially only 2 TB of physical disk space is allocated. As the amount of stored data increases, the storage system automatically allocates more space (up to the 4 TB maximum size). And, even though only 6 TB of space is available on the storage system, the administrator is able to add 2 virtual disks with a total potential capacity of 8 TB.
Allocation alarms and email notification are used by the administrator to monitor data increases and send email notifications.
You can use SSSU to view the amount of virtual disk space that is allocated and used.
NOTE: SSSU displays the percentage of allocated space used. This allocation level is rounded down to the whole number.
34 Provisioning storage