If you don't test your backups, then they're not backups.

yup, the assertion that both failing is highly unlikely is under the assumption that you are checking the status of each copy regularly.

In fact for any disk, it is important to have a script that reads all the data at least every couple of months. It will force the bad sectors to be identified or to be notified you have a bad disk before things get worse.

Yeah, agree. And I am not talking about enterprise level of reliability. More like personnal / small office.

But for anything above a few TB, running your own hardware will be way cheaper if you take say a 5y horizon. Disks are so large today that you don't need a big config. In fact you might even keep two copies to reduce the risk.

Of course there is the occasional trip to the datacentre. I made that mistake. I pay more in uber than I saved by picking a datacentre far away.

Do you need co-location though? I dropped an HP Microserver at a friend's place, which backs up snapshots of my main backup server at home daily. Seems to work well so far, at quite limited costs. Since my main backup server also backs up his NAS we both win. Since all backups are encrypted there is also little privacy risk from theft (or snooping on one another).

With 1Gbps symetrical connections slowly becoming more frequent this would be a much cheaper alternative (assuming you only run it for backups, I also run a mail server and some websites). But in London it is not very practical. I know very few people who have really fast broadband.