You can read or write these entire drives in under a day. It wouldn't take a month.

The month was exaggerated for effect.

Best case is 12TB / 254 MB/s ~12 hours, * 2.5 = over a day.

However, random reads are a lot slower.

Random reads don't care how long it takes to read an entire disk.

Very few things do, really. It's pretty much just rebuilding a RAID or reorganizing your data storage hardware that care about full-disk transfer speed, and in those cases two days isn't a big deal.

There are great ways to mitigate the problem, but disks still get fragmented. So, at best we can say it's probably not an issue the majority of the time.