Aside from the issue of emptying data cells in SSDs, there is also the fact that each cell has a limited lifespan and can only be written and erased so many times before it fails. Most normal use won't reach that number of rewrites for years. But it's not always that easy to predict. To deal with that, the SSD controllers are basically little computers that run a very complex management system to shield users from this inherent volatility. These drives typically have an additional 10-20 per cent capacity that they use as memory cells gradually fail. Each bad cell is reallocated a good block from this secret cache of spare cells. But once this cache of spares is used up, that's it. It will cease to work, and sometimes in a spectacularly rude way. Most SSDs will go into a read-only mode, which is fine. But many, for reasons the manufacturers struggle to explain why, will simply shut down forever and refuse to power up at all.
If you are wondering why I'm so well versed in the potential tragedy of relying on SSDs. It's from personal experience. Eight weeks ago I bought a shiny new Macbook Air, a long overdue upgrade from my trusty Macbook Pro. Four weeks later it developed a problem, so I ran my usual utilities. To my horror nothing could fix the bad node, and the drive was useless until I reformatted it, losing everything on there.
The four types of backup you need to be safe: online, local, live & archiving
Thankfully I have a belt-and-braces mentality when it comes to backup. Actually it's belt, braces, and two more belts, as it's a four-pronged approach. So even though one of the backups failed, I still didn't lose any data and had a relatively painless recovery.
It's that response to data loss that I want to share. Because even if you have a backup, these days a single backup is probably not enough to save people from all the pain a catastrophic storage failure can cause.
You can get away with only using one, or maybe two of the backup methods I'm about to outline here. But each has its strengths and weaknesses, so it's for you to decide where you want to skimp if you must.
Online backup is very popular these days, as it offers an inexpensive way to secure your data. The downside of online backup is that the initial backup is slow, and restoring anything more than a few files can take a long time. It's definitely worth doing, but if you need to minimise your downtime you need something quicker.
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