time capsule erase

A 7 Pass Erase is the same as a Zero Out Data Erase, which replaces everything on the Time Capsule disk with zeros.....except that the 7 Pass process will repeat itself 7 times instead of making one pass.

A single Zero Out Data Erase is all that users will ever need to securely erase the disk. There would really be no need to run a 7 Pass Erase unless you are paranoid about security. A 35 Pass Erase.....which is a Zero Out Data Erase that repeats 35 times......is only for the extremely paranoid users.

The question here would be "when" the power outage occurred. If it happened during the first pass, then the entire disk has not been securely erased. If the power went out after a few zero out data passes had already completed, then there would be no need to erase the disk again.

To extend what Bob Timmons writes...

Multi-pass erasures are from the era of floppy disks, and for hard disks from that same antediluvian era or earlier.

Remember those floppies? The head-positioning on those floppy drives was really sloppy.

Newer disks have what is called embedded servo positioning, meaning the heads are always on track.

Unlike floppy disks. Which used external positioning, and weren't always reliably on track after a seek.

With HDDs from the past 25 years or so and with the embedded servo positioning, a single pass erasure will work for what you want here.

And with SSDs, even single-pass erasure won't do what most folks expect. SSDs don't have a way to overwrite a sector. Each write goes to a new and different sector, not to the one that held the previous data. For security, SSDs thus depend on storage encryption, TRIM—which erases the previous contents of the sector—and a Secure Erase command for those devices that support that.

If you want to be yet more certain of the HDD or SSD erasure, physically destroy the device.