Brian from Backblaze here. > how do you determine which drive to swap Every two minutes we query every drive (all 45 drives inside the pod) with the built in

Brian from Backblaze here. > how do you determine which drive to swap Every two minutes we query every drive (all 45 drives inside the pod) with the built in linux smartctl command. We send this information to a kind of monitoring server, so even if the pod entirely dies we know everything about the health of the disks inside it up until 2 minutes earlier. We remember the history for a few weeks (the amount of data is tiny by our standards). Then, when one of the drives stops responding, several things occur: 1) we put the entire pod into a "read only" mode where no more customer data is written (this lowers the risk of more failures), and 2) we have a friendly web interface that informs the datacenter techs which drive to replace, and 3) an email alert is sent out to whomever is oncall. Each drive maps has a name like /dev/sda1 and these drive names are reproducibly in the same location in the pod every time. In addition (before it disappeared) the drive also reported a serial number like "WD‑WCAU45178029" as part of the smartctl commands which is ALSO PRINTED ON THE OUTSIDE OF THE DRIVE. TL;DR - it's easy to swap the correct drive based on external serial numbers. :-)