It’s official. My 10-month-old 256GB solid-state disk is dead. After the trials of the past two weeks, which I initially blamed on everything but the disk, I’ve had confirmation that the unit is well on the way to total failure.
At the Genius Bar the faulty drive was diagnosed as terminal and a replacement will be installed within the next four days.
The lesson I’ve learned from this episode is that SSDs behave in a different way to HDDs. Usually a hard drive will fail catastrophically and not hobble along, causing random errors, as this SSD has done.
If you experience unusual behaviour with your SSD-equipped Mac I would suggest a disk verification before suspecting software or settings.