With our exponentially increasing data, efficient storage and management of data is of paramount importance to organizations. To aid in this, a new category of software, referred to as storage management software (SMS), has recently been unveiled.

However, there has been some confusion in the industry as to whether SMS is new, or just another offering of HSM (hierarchical storage management). While both solution types keep frequently accessed data on high performance storage (usually the most expensive), and both migrate inactive data to other types of storage (usually much less expensive), clear differences exist in the way that both solutions achieve this objective.

Transparency is key

800px-Interior_of_StorageTek_tape_library_at_NERSC_ derrick coetzee wikimedia.jpg
StorageTek robot tape library at NERSC, Lawrence Berkeley National Laboratory – Derrick Coetzee / Wikimedia

A common vocabulary is vital to communication. As such, whenever a file is moved, stub files, symbolic links and HTML links are the “bread crumbs” left behind providing identifiable ties to the original files. These represent the most transparent method by which the user or application can retrieve specific files as easily as possible. The level of transparency based on methodology is a key differentiator between HSMs and Storage Management Software.

HSM characteristics

HSMs make migrated data appear to be online by mapping nearline storage, including tape storage and the “cold” tiers of cloud storage. With a tendency for long latency, nearline storage can be subject to longer waits on retrieval. If applications do not receive the data requested within the expected timeframe, they will time out. HSMs typically use stub files, which resemble and often contain the first bytes of the original file. The stub file responds to the read request and the HSM enables retrieval of the rest of the moved file. HSMs are highly dependent upon the operating system and have to be upgraded along with it, so it essentially becomes part of the system. HSMs usually have kernel code and offer no ability for the application or the user to see that a file has been moved.

HSMs work well in high performance computing (HPC) “time-out tolerant” or “HSM aware” environments, but are not a good fit for all environments. HPSS and DMF HSMs are successful solutions, though they can also be complex, expensive and require lots of resources. However, when deployed in the right environments, these HSM solutions are effective.

SMS benefits

With a few exceptions, SMS solutions tend to require less budget, headcount and infrastructure than HSMs, and operate well outside of the file system. In contrast to HMS, SMS is less complex and more compatible with a wide range of applications and use cases. SMS is more likely to utilise symbolic links and/or HTML links (which work quite differently from stub files as well as from each other), to find the moved data.

When the SMS replaces an original file with a symbolic link, a read can simply be redirected to where the file has been moved. This is especially beneficial when moving infrequently accessed data off of primary storage (high-speed disk or SSD), to a lower tier of storage like secondary NAS disk. Although most applications can tolerate the small increase in latency, this methodology does not work well with tape or low response level cloud (Amazon Glacier is one example). And this is where the HTML links demonstrate key benefits, because they are designed to specifically support longer latency storage mediums, such as tape or the cold tiers of cloud.

This functionality also benefits users because once an HTML link has been set in place of the migrated file, an HTML page is automatically presented, which provides information as to how, when and where the file has been archived. The user can then seamlessly commence a restore from tape or recall the file from cloud without the necessity of contacting IT for assistance. So when it comes to file transparency, SMS solutions present some additional benefits when compared to HSMs.

Data protection

Data protection is the final differentiator between HSMs and storage management software. Unlike HSM solutions, storage management software has been created with a focus on data preservation as well as primary storage offload. SMS enables multiple copies of the original, with the ability for these to be stored in numerous locations and various storage types. So in addition to moving infrequently accessed files from expensive primary storage to lower cost NAS, users can significantly increase data protection by sending a copy to an on-premises tape library, to offsite tape storage, or to the cloud for disaster recovery.

The capabilities of storage management software can allow organizations to decrease primary tier storage volumes, increase overall performance, and shrink backup windows, while also eradicating the need for more primary storage purchases. Additionally, SMS can also provide assurance as to the long-term protection of and perpetual access to the less active data via multiple copies to a range of storage mediums.

So when deploying a data tiering solution, it is vital that organisations give full consideration to the differentiation between each solution type, as well as weigh the benefits of individual solutions that fall into each category, so that the best match can be found to suit the specific needs of the organisation.