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9. Thin Provisioning
This chapter describes an overview and operations of thin provisioning.
9.1. Overview
Nowadays, thin provisioning is a hot topic people talk about in IT management and storage
industry circles. To contrast thin provisioning, it naturally comes to mind with the opposite
term – thick or fat provisioning, which is the traditional way IT administrators allocate
storage space to each logical volume that is used by an application or a group of users.
When it comes to the point of deciding how much space a logical volume requires for three
years or for the lifetime of an application, it's really hard to make the prediction correctly and
precisely. To avoid the complexity of adding more space to the volumes frequently, IT
administrators might as well allocate more storage space to each logical volume than it
needs in the beginning. This is why it's called thick or fat provisioning. Usually it turns out
that a lot of free disk space is sitting around idle. This stranded capacity is wasted, which
equals to waste of investment in drives, energy usage, and general inefficiency. Various
studies indicate that as much as 75% of the storage capacity in small and medium
enterprises or large data centers is allocated but unused. And this is where thin provisioning
kicks in.
Figure 9-1 Traditional Thick Provisioning
Thin provisioning sometimes is known as just-in-time capacity or over allocation. As the
term explains itself, it provides storage space dynamically on demand. Thin provisioning
presents more storage space to the hosts or servers connecting to the storage system than
is actually physically available on the storage system. To put it in another way, thin
provisioning allocates storage space that may or may not exist. The whole idea is actually
another way of virtualization. Virtualization is always about a logical pool of physical assets