You might wonder why posting about this glitch in Gmail. It is this part that makes it relevant for data folks:
how could this happen if we have multiple copies of your data, in multiple data centers? Well, in some rare instances software bugs can affect several copies of the data. That’s what happened here. Some copies of mail were deleted, and we’ve been hard at work over the last 30 hours getting it back for the people affected by this issue.
To protect your information from these unusual bugs, we also back it up to tape. Since the tapes are offline, they’re protected from such software bugs.
The message is clear: replication is not enough to ensure data safeness. For all sensible data you must have offline copies and data recovery strategies.
Original title and link: Gmail back soon or Replication vs Data Recovery (NoSQL databases © myNoSQL)