Backblaze

When is Backblaze backup deleted?
[Internal Drive]

|<- 60 days ->|
+-------------------------+
^ ^
| |
PC goes offline backup for internal drive is delete
(backup for external drive is deleted too)
[External Drive]

*If PC keeps online:

|<- 30 days ->|
+-------------+
^ ^
| |
Drive goes offline backup for external drive is deleted
(detached)

+-- external drive keeps offline (detached)
*If PC goes offline: |
v
|<- less than 60 days ->|<- 30 days ->|
+-----------------------+-------------+
^ ^ ^
| | |
PC goes offline PC goes back online backup for external drive is deleted
(Edit)

https://help.backblaze.com/entries/20202057-best-practices
"if your computer does not contact the Backblaze datacenter for six months then your account will be cancelled and the mirrored copy deleted from the Backblaze datacenter."

http://www.backblaze.com/edrive.html#unplugged
"re-attach the hard drive at least once every 30 days. [...] You can then leave your computer off and unplug your external drive for six months"