What you will learn in this tip: Thin provisioning is a relatively recent technology for the allocation (or provisioning) of disk storage to systems. This technical tip provides an overview
of storage thin provisioning, some of its benefits and potential downsides.
What is thin provisioning?
At a high level, thin provisioning storage is the ability to define a LUN or volume of a certain size on a storage area network (SAN) storage array and make it appear larger than it is to the server to which it is allocated. You can think of it as a disk storage “line of credit” for servers. In reality, storage thin provisioning allows you to allocate a certain amount of SAN storage to a server (e.g., 200 GB), allowing it to automatically grow to a predefined limit (e.g., 800 GB) while keeping the entire process transparent to the server. To that server, it looks like it has 800 GB of disk space available if needed. If the storage space allocated is not needed it is not used.
The benefits of thin provisioning storage
Thin provisioning storage can help delay additional capacity purchases, which can cut costs as disk prices keep dropping. Here's an example where thin provisioning storage can help: You do not necessarily have the capital budget to purchase all the disk capacity your IT systems or servers might need in two or three years from now on day one. You may also have a good idea what that future storage capacity requirement will be, but not know for sure which systems will need more storage first.
Without thin provisioning, storage administrators have to allocate storage based on immediate requirements and leave some room for growth in an unallocated storage pool based on additional capacity available. As individual applications need more storage, capacity has to be manually allocated from that pool. If a system did not use all its allocated storage, it has to be unallocated and returned to the pool and made available. When storage capacity on the array runs out, you need to purchase additional disk, add it to the pool and allocate it to systems as needed.
Thin provisioning storage is helpful in these types of situations because it allows you to pre-allocate storage without actually committing the physical capacity. Thin provisioning eliminates the need to decide ahead of time how much storage each system will need. When you allocate a 200 GB thin LUN that looks like 800 GB to an application, you are essentially allocating 200 GB of physical disk space, which allows it to automatically grow to 800 GB without having to do anything about it. The system uses the capacity it needs, but any space that goes unused remains available to other systems. This eliminates the need to commit physical storage to specific system to support growth.
As an added bonus, vendors such as EMC Corp. with Unisphere and Hewlett-Packard (HP) Co. with 3PAR, provide the ability to shrink or reclaim storage capacity from a thin LUN that may have been temporarily used by a system but no longer needed.
Thin provisioning can greatly simplify storage capacity management tasks. In addition, the ability to grow and reclaim storage capacity is very much aligned with the cloud concept which promotes “elasticity” as one of its most valuable attributes.
The downsides of storage thin provisioning
Sometimes thin provisioning may not yield the results a storage administrator is looking for. For example, there might be a temporary sudden increase in storage demand that may push cumulative storage requirements for individual systems beyond the storage array’s total capacity. This might be due to lack of planning or communication between application owners and storage administrators (but you can set alert thresholds so that you’re not likely to be surprised).
There are also applications that might not work as well with thin provisioning if the storage administrator is not careful. Take for instance database applications (DBAs) for which pre-allocated table space is created. If a DBA decides to create datafiles as large as the storage space appears (800 GB in our earlier example), the entire disk space will end up being used, nullifying the benefits of thin provisioning.
Not just for the enterprise
It is worth noting that while storage thin provisioning has significant advantage for large-scale storage users, the technology is also available to small- to medium-sized businesses (SMBs) from a few vendors. Some examples include EMC’s new VNXe 3100, which supports thin provisioning and can be configured with as few as six drives to start and scale up to 96 drives. Similarly, NetApp offers the entry-level FAS2020, which supports thin provisioning as one of its standard features.
Overall, thin provisioning is a storage feature aimed at improving storage utilization by eliminating over-allocation. It also simplifies storage management by allowing systems to grow their storage requirements without having to micro-manage capacity allocation.
About this author: Pierre Dorion is the data center practice director and a senior consultant with Long View Systems Inc. in Phoenix, Ariz., specializing in the areas of business continuity and DR planning services and corporate data protection.
This was first published in February 2011