Are they using big disks and having to resilver or re-do their RAID setup across the added drives, requiring everything on the disks to be read and re-written?
> However, we did not anticipate that the expansion process would require the server storage to be temporarily offline.
This is embarrassing. Somebody made a big mistake of the “mistakes like this shouldn’t be made” category. Like not an accident or fat finger or a bug, but engineers not understanding fundamentals of how a system worked and having none of the processes in place to to dry runs in non production or any of the other things that would protect against something like this. Really questionable to trust an organization that makes a mistake like this.
You have no idea what happened.
Protecting against "something like this" often introduces complexity and failure cascades that are much more harmful than a simple system being offline.
In fact, I would consider it a feature if uptime was deliberately sacrificed for simplicity and data integrity.
I wish Manu the very best and will consider it not a failure but a success if this array/subsystem/whatever comes through without data loss.