Posey's Tips & Tricks
Are Storage Array Snapshots a Viable Backup Substitute?
While storage array snapshots offer quick, hardware-level data protection, they are not a standalone substitute for traditional backups due to limitations in protection, management and retention capabilities.
Most organizations that still maintain on premises workloads tend to rely on traditional backups. While these backups are often the best choice for protecting the organization's data, there is another option. Many storage arrays offer a built-in snapshot feature that allows data to be protected at the storage level, without the need for a backup application. Better still, storage array snapshots almost always offer better performance than traditional backup applications, because they work at the hardware level. Even so, storage array snapshots aren't the perfect backup alternative that they might seem to be. There are some things that organizations must consider before making the switch.
One of the most important considerations to take into account is that storage array snapshots tend not to provide the same level of protection as a normal backup. When you create a backup, you are creating a restorable copy of your data in another location. Storage array snapshots on the other hand, are created within the storage array itself. This means that if something were to happen to the storage array (such as being dropped or being struck by lightning), the snapshots would probably suffer the same fate as the data that they were protecting.
It's also worth noting that some storage arrays write snapshots to supplementary disks within the array, while other arrays create snapshots on the same disks where the original data resides. Snapshots that exist on the same disk as the data can be created and restored almost instantaneously. The tradeoff however, is that if a storage volume were to become corrupted then the corruption may put the snapshots at risk. Additionally, storing the snapshot data on the same disks as the original data may affect a volume's performance and reduce its available storage capacity. This is especially true if the data that is being protected has a high change rate.
If you are considering using storage array snapshots to protect your data, there are some logistical issues that you will need to consider. The first of these issues is that of managing the arrays and their snapshots. Most storage array vendors offer management software that can be used to manage an organization's collection of storage arrays. However, this software is almost always proprietary, meaning that the software is most likely going to be vendor specific. If your organization uses storage hardware from a variety of vendors, you may find that you have to manage each vendor's products separately.
Another consideration is that some, but certainly not all, storage vendors require an additional license in order to use an array's snapshot feature. As such, organizations must determine if they are subject to any additional licensing requirements, and if so, what those licenses will cost.
Retention policies are another important consideration. Again, each storage vendor has its own way of doing things, but some vendors will allow for long term snapshot retention, while others only allow for brief retention periods. There are also storage vendors who do not enforce a specific age limit for snapshots, but rather base the retention periods on the available capacity within the array and the rate at which data is created or changed.
One more consideration that you must take into account is the type of data that you are trying to protect. Depending on which vendor's products you are using, you may find that array snapshots cannot be used with certain workloads, such as databases or virtual machines.
Given all of the potential issues that I have just outlined, it may seem as though using storage array snapshots is a bad idea. However, array snapshots do have their place. As previously noted, these snapshots can make it possible to almost instantly roll back a volume to a previous state. The important thing to remember however, is that array snapshots were never intended to replace traditional backups. Instead, they are best used as a supplementary data protection solution. For example, if you need to restore an entire volume then it's almost certainly going to be faster to apply an array snapshot than to restore a traditional backup. However, if you need to recover a specific item from within a volume (such as a file, a virtual machine, or some other type of data) then you may find that array snapshots lack the necessary granularity. As such, my advice would be to use array snapshots when it makes sense to do so, but to use them as a way of supplementing your existing data protection strategy rather than replacing it.
About the Author
Brien Posey is a 22-time Microsoft MVP with decades of IT experience. As a freelance writer, Posey has written thousands of articles and contributed to several dozen books on a wide variety of IT topics. Prior to going freelance, Posey was a CIO for a national chain of hospitals and health care facilities. He has also served as a network administrator for some of the country's largest insurance companies and for the Department of Defense at Fort Knox. In addition to his continued work in IT, Posey has spent the last several years actively training as a commercial scientist-astronaut candidate in preparation to fly on a mission to study polar mesospheric clouds from space. You can follow his spaceflight training on his Web site.