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Storage Thin Provisioning And Performance

Updated on December 14, 2011

What Is Thin Provisioning?

Keep your data thin like one of the thinnest buildings in the world seen in the photo here. The definition of thin provisioning can be applied in general to a broad application of resource allocation but in terms of storage area networks (SANs) and other data storage virtualization technology thin provisioning is defined as using virtualization technology (such as a storage hypervisor) in order to give the illusion that the there are more physical data storage resources available than actually exists. In most datacenters which incorporate a shared storage environment the ability to have thin provisioned disks and virtual disks has become a standard feature and a must-have SAN technology in order to realize high performance gains and follow best practices. Thin provisioning allows an IT department to define storage volumes or LUNs that can be over-allocated allowing the benefit of being able to grow easily in the future with the addition of further hard drives/SSDs while presenting the storage administrator with the disadvantage of having to monitor free space closely to insure that resources do not become over utilized resulting in errors and out of space issues. Of course, any competent enterprise storage engineer should already have alarms and monitors in place to check all critical values regarding storage capacity free space and most SAN devices which include thin provisioning have many such auxiliary features built-in making the job of data management easier. Such dynamic LUN provisioning is a feature found in many storage virtualization and storage appliance vendors from Netapp Data OnTAP to EMC Virtual Provisioning to Hitachi Data Systems Dynamic Provisioning and also the "storage hypervisor" software of Virsto. There may be different nomenclature and some proprietary and trademarked product naming conventions, but the concept of thin provisioning storage is global.

Thin Provisioned

photo by 29735106@N04 on Flickr
photo by 29735106@N04 on Flickr

SAN Thin Provisioning Benefits

So it should be clear that one of the pros of dynamic lun provisioning is that it lowers the TCO of a datacenter's overall storage architecture. For example an overallocation ration of say 10:1 (10TB of physical capacity versus 100TB allocated density) with the current prices of enterprise hard drives and SSDs could create a savings of over a 100 thousand or more in the IT budget of a corporation or institution. This includes an operational expense reduction in datacenter power consumption through less drives which require less electricity and cooling costs. Future costs of enterprise hard drives will be lower due to the Moore's Law of computer hardware trends. Storage management is simplified through GUIs and interface that utilize the same free pool of resources to pull needed increases in LUN sizes and overall thin provisioning can provide a more versatile and mobile SAN that can adapt to demands as they arise rather than being hard coded based on initial storage roadmaps and blueprints.

Thin Provisioning Disadvantages Defined

As it seems that with every good innovation there are bound to be some drawbacks from storage area network strategies which make use of thin LUN provisioning rather than conventional "thick" provisioning for virtual volumes. One of the larger disadvantages is the fact of how to deallocate space effectively so that the storage device will know that there is now free space in the pool and be able to use it for other storage virtualization volumes. Otherwise, once allocated to full capacity the thin provisioned volume would essentially become thick provisioned with no method to revert. Solutions have been presented. One is zero page reclamation which effectively makes the assumption that a data page filled with all zeros is not in use and can be reclaimed. Other intelligent solutions have made it to market such as Symantec's Thin Reclamation API and the Veritas Storage product. Further advances have been made in that past year or so but it is important to check what type of thin reclamation is built-in to your storage options before making the purchasing decision. Also, be aware that things can be complicated when used in a heterogeneous storage environment and in particular with tiered storage solutions. A second disadvantage can be seen if thin provisioning is implemented in such a way that performance metrics suffer. Enterprise SANs are looking for maximum IOPS but disk operations can be slowed if processing power must be given to thin provisioning and reclamation processes.

Thin Provisioned Format May Be Ideal

In conclusion, there are quite a few problems and areas to look at before making the decision to implement thin provisioned volumes over normal data volumes but in the end it may be beneficial to go with such a solution. There are certain use cases where it definitely makes sense while other times it would not be feasible at all. Just make sure you are solving a technical problem if you decide that thin provision is the answer and not solving a business problem. It should probably not be seen as a way to simply implement capacity that you cannot afford but rather part of a larger solution that when combined with other features like data deduplication, snapshots, raid levels, hot spares, wear leveling, and scalability can bring datacenter improvements at a time when "Big Data" is becoming the norm.


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