Thin provisioning

This technology is one of the options for storage virtualization, which can be used to increase the return on storage resources and improve profitability. Thin provisioning is often used to reduce the amount of unused space on devices that are not utilized by applications at a particular time.

Usually storage devices are not 100% full and do not use all the system resources. But it is always necessary to organize work in such a way that there is a reserve of free disk space – for the stability of system operation and maximum readiness for rapid data growth.

Such, in fact, unused disk volume was traditionally allocated for absolutely all the volumes connected to the storage system. Those logical volumes, which have exclusive disk space in full at the current moment of the storage system operation, are called “thick” volumes among system administrators.

The above-described model of volume disk space usage first appeared in the times of creating the first data storage systems. It has not lost its relevance until now.

The principle of how Thin provisioning works

If we take Thin provisioning apart, the concept of this solution is as follows:

• When a logical volume (LUN) is created, the disk array is not fully allocated for data.

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• The LUN LBA (backend physical address) matching table is initiated.
• The storage administrator specifies the maximum allowable volume size and the limit of its data occupancy, when it reaches this limit, the corresponding message will be displayed.
• At this point, the new blocks will be blocked by the new disk blocks.
• New blocks of the logical volume for storing information are allocated as it fills up.

As soon as the server releases the data blocks, a directive will be sent to the storage system about the free blocks and the need to return them to the common pool.

Implementation of Thin provisioning in practice:

1. The server (host) sends a request to the storage system about the current volume size (SCSI Read Capacity) and allocates the limit volume from the total disk volume, which was previously set by the administrator.
2. On a storage system, the sum of the volume limits on all volumes can be much larger than the physically available space on the storage system.

Once the storage system receives the SCSI Read Capacity command (can be encapsulated in FC stack, SAS, iSCSI, etc.), it allocates another “chunk” from the free disk capacity and writes the information there from SCSI Write.

Thin provisioning technology should have support not only on the storage system side, but also on the operating system side, host block device drivers. In modern operating systems (Windows, Linux, etc.) such support has already existed for a long time.