One of the most fundamental truths of enterprise computing is that your current storage will eventually become outdated and inadequate. At the same time, the storage used to service mission-critical workloads is constantly in use and generally cannot be taken offline for upgrades. Fortunately, when it’s time to upgrade storage for appliances, there are many paths toward non-disruptive upgrades.
It is tempting to think of storage upgrades as being synonymous with capacity upgrades. While capacity upgrades are indeed a way to upgrade storage for appliances, there are other types of storage upgrades that need to be considered. Here are four types to consider, including the ability of each to support non-disruptive upgrades.
Storage Controller Firmware Upgrade
Storage vendors periodically release firmware revisions that correct bugs, introduce new functionality or address security issues within storage controllers. As with any other type of storage upgrade, it is important to be able to apply these firmware revisions without disrupting business operations.
In most cases, storage vendors leverage controller redundancy as a mechanism for achieving a non-disruptive firmware upgrade. The process works by placing one controller into maintenance mode, performing the upgrade, and then bringing the controller back online. The process is repeated in round-robin fashion until the upgrade has been applied to all of the controllers. Some vendors automate this entire process, while others still require firmware updates to be performed manually.
Storage Controller Replacements
Just as it is important to be able to upgrade your storage controller’s firmware without taking the storage offline, it is equally important to be able to replace an aging storage controller with a newer model without causing any down time in the process.
On the surface, storage controller replacement might seem to be a non-issue. After all, if you can take a storage controller offline to upgrade its firmware, then taking a storage controller offline to replace it with a newer version should work in essentially the same way. However, there are a few things that you need to consider before replacing a storage controller.
First, you must consider whether the new storage controller is going to be backward-compatible with the controllers that you have in place. In other words, can you take a storage controller offline, replace it with a new model, bring it online, and have the storage cluster accept the new controller as if nothing happened?
Some vendors do allow for seamless storage hardware upgrades in the way that I just described. Oftentimes, though, you will be limited to using only those features that are supported by the remaining legacy controllers until all of the controllers in the cluster have been replaced. At that point, you can begin using the new features.
Regardless, it is important to check the vendor’s upgrade path. Some vendors still require that controller replacement be handled as a migration rather than as an upgrade, meaning that there is a point in the process where you have to tell the storage cluster to begin using the new controllers that have been brought online and to stop using any remaining legacy controllers.
A second important consideration is whether your new storage controller is going to continue to recognize the logical disk structures (such as RAID sets) that you currently have in place. It would be rare, but I have heard stories of upgrades that required storage to be completely reprovisioned.
Disk Firmware Upgrades
It is also worth considering whether or not you can perform a non-disruptive firmware upgrade on the actual disks. As of right now, many storage vendors allow for non disruptive firmware upgrades for SSDs, but similar support for HDDs is somewhat less common.
Data Migrations
Of course the holy grail of non-disruptive storage upgrades is non disruptive data migrations. Not all that long ago, non-disruptive migrations of anything other than stateless systems was difficult, to say the least. Today, though, there are storage vendors that offer viable solutions for migrating live storage without disruption and with minimal performance impact.
Conclusion
These are just a few of the things that you should look for with regard to non-disruptive upgrades with storage for appliances. Others include--but are certainly not limited to--storage shelf additions and replacements, controller additions and network port firmware upgrades.
