You can replace the offline/failed drive at any time. The data is being reconstructed on to the spare drive.
At the CLI you can run:
GrpName>member select MEMBERNAME show
Where MEMBERNAME is the name the array that's rebuilding.
E.g. I have a member named: PS6210E
GrpName>member select PS6210E show _____________________________ Member Information ______________________________ Name: PS6210E Status: online TotalSpace: 33.74TB UsedSpace: 817.56GB SnapSpace: 1.57GB Description: Def-Gateway: 100.85.224.1 Serial-Number: Disks: 24 CN-04FMJV-70821-34A-07GR-A00 Spares: 1 Controllers: 2 CacheMode: write-back Connections: 162 RaidStatus: ok RaidPercentage: 0.000%
The RaidPercentage will show you the rebuild percentage.
The 70-0450 part number is for the controller, a Type 11. You might want to use the Array model number instead. E.g. PS6100E, or X, or XV. Makes is easier to identify model and drive types when asking for help.