HP StorageWorks SAN Virtualization Services Platform Best Practices Guide (5697-0935, May 2011)

A Thin provisioning and operating system interaction
Executive summary
Thin provisioned storage allows the SVSP administrator to pre-plan user capacity needs and allocate
virtual storage based on the expectation, but only consume the actual disk space the user is
accessing. As a result, the administrators no longer have to concern themselves with wasted storage
not currently in use by the users. The purpose of this section is to provide an overview on the best
practices for setting up Thin Provisioning (ThP) on the SVSP.
ThP overview
System administrators typically provide themselves with a lot more storage than required for various
applications due to planning ahead for growth. For instance, an application may require five
virtual disks with 650 GB of total actual data, but based on some analysis, or at the request of the
department, the system administrator has created a 3 TB virtual disk, allowing for data growth. If
a virtual disk is created with 500 GB of space, this space is typically dedicated to that application
virtual disk and no other application can use it. However, in many cases the full 500 GB is never
used, so the remainder is essentially wasted, which is a major problem while managing storage
capacity and is often referred to as stranded storage.
The inefficiencies of traditional storage provisioning can impact capital costs and storage
administration resources negatively. The most obvious issue is the amount of storage that remains
unused and, therefore, increases the total cost of ownership. Additionally, since this allocated but
unused storage capacity cannot typically be reclaimed for other applications, customers have to
buy more storage capacity as their environments grow, increasing cost even further. At some point,
customers may actually be required to buy a completely new storage system in addition to the one
they have in place.
Results from multiple surveys conducted by several analysts and storage companies targeting
enterprise storage have uncovered several limitations regarding traditional storage provisioning
methods. The highlights of the surveys are as follows:
• Over 50% of the customers were aware that they had stranded and unused storage capacity
due to inefficient provisioning methods.
• Over half of these customers had between 31–50% of stranded and unused storage. For
example, if they had 10 TB of storage capacity, then 3.1−5 TB was stranded.
• Almost half of the total users had to buy an additional storage system (array) because they
could not utilize their stranded storage. This means that although these customers had unused
storage capacity they had already paid for, they needed to buy a new storage system to meet
the needs of their business.
• Close to one third of users are planning to buy an additional storage system in the next 12
months because they cannot access their stranded storage.
• Over 75% of users felt that storage provisioning was a time and resource drain on their IT
organizations.
ThP and its value
Thin Provisioning is a technology that allows large virtual disks to be presented to hosts, which are
backed up by a storage pool of significantly less actual storage (see below). The virtual disk
presented to the host appears to have much more capacity (virtual capacity) than is actually the
case. Pages of actual storage are allocated from the storage pool as needed to accommodate
writes to the virtual disk.
70 Thin provisioning and operating system interaction