Network storage devices make it incredibly easy to upgrade your hard drives using their hot-swappable mechanism. You simply pull out the bad drive and slot in a new one. Wait for the rebuild to finish, and you're done. It's basically plug-and-play, and the NAS reassures you enough that there is a very tiny chance of anything going wrong. There are a bunch of hard drives that are compatible across NAS brands, so these drive upgrades start to feel mindless at this point.

While it sounds quite easy, most users don't realize that a lot of NAS disasters happen during the upgrade itself. It is perhaps the most vulnerable moment for the NAS in its entire life cycle, and a lot of us learn about it only while it's happening.

It's about how people think about upgrades

Upgrading drives is far from routine maintenance

One of the biggest mistakes people make when upgrading their NAS drives is treating them like a simple storage upgrade instead of a system-level change. They tend to care too much about capacity and even price, while everything else is assumed to be easily handled by the NAS operating system.

Unlike a simple USB enclosure, a NAS is much more complex, where several elements, including the drives, the controllers, firmware, and the workload, come together to complete a system. When you pull out a drive and try to replace it, besides adding more space, you are also forcing the entire system into a stressed state where it has to rebuild all the missing pieces, and the chances of failure statistically grow exponentially here.

And the system also does a good job of hiding all the complexity behind a simple interface that shows you a watered-down progress bar. This overconfidence in the system that it itself portrays is similar to walking on thin ice in reality.

Compatibility lists and rebuilds are the riskiest

That's one way of stress-testing your NAS

Your NAS may be compatible with a list of drives that your vendor publishes. This generally means the drive is recognized by the NAS and won't break any operations like RAID and SMART metrics. But when you mix and match drives with different firmware generations, capacities, error recovery behaviors, and other characteristics, they can technically coexist and are even the norm. But during rebuilds, those minor differences do matter. The system would work just fine until one day it had had enough of one of those older drives and just gave up.

But a bigger culprit, or rather the stress point, is the rebuilding process. During this session, the remaining drives in the array are pushed into sustained, near-constant activity. Depending on the volume, it can go on for hours or even days of continuous reads, calculations, and writes. The drives that seem perfectly healthy until now are suddenly operating under severe conditions that they rarely see in normal use.

That is the very reason why drive failures happen during upgrades rather than before. Older drives are especially vulnerable here. Even if they appear alright day-to-day and pass SMART checks, these abnormally harsh conditions expose marginal sectors and weak areas and only aggravate them.

The longer these drives spend rebuilding, the longer they stay in this degraded state. And the longer they stay degraded, the higher the chance of a possible failure.

What can you do?

It's the timing, not the technique

If you ask anyone the reason they are upgrading their NAS disks, what you'll get back is usually along the lines of, “I'm running out of space.”

That's quite common, but it's also the worst time possible to upgrade your NAS drives. A system upgrade of such high magnitude should happen in a more controlled environment, where the pressure of running out of space isn't there. Going for rebuilds in such a state leaves no margin and little patience for slow rebuilds. The system has no wiggle room in case something goes off track.

During this process, if you don't already have an off-site backup in place — the very reason we stress off-site backups — even RAID won't be able to provide you enough safety if you encounter a major drive failure on your system. A good measure would be to give your NAS, and even yourself, enough margin before deciding to upgrade the drives. Do not wait for the last moment to make it happen. Keep a watchful eye on the system and prepare for it in advance.

The idea is to minimize the time spent rebuilding, and therefore the time the drives are under stress, so that you maximize your ability to walk away without panic in case something goes wrong. And you should also have an actionable plan before you start to ensure data safety in case another drive fails in the middle of a rebuild. I know I am saying it again, but this is where an updated off-site backup would come into play. Take it very seriously.

Stop mistaking RAID for backup

RAID serves a particular purpose on the NAS, and that is to provide redundancy — that's it. It can save your day if one of the drives fails, and that's where the convenience of hot-swappable drives comes into the picture. But it's not the kind of insurance that a backup is. A frequently updated backup system will save you even in cases where more than one drive fails. Prepare a solid backup strategy that also includes RAID so that you are protected on all fronts and vulnerable nowhere.