Brings the selected offline disk to the online state. Syntax: ONLINE DISK NOERR NOERR For scripting only. When an error is ...

    Brings the selected offline disk to the online state.

Syntax:  ONLINE DISK [NOERR]

    NOERR       For scripting only. When an error is encountered, DiskPart
                continues to process commands as if the error did not occur.
                Without the NOERR parameter, an error causes DiskPart to exit
                with an error code.

    This command operates on a single disk. A disk must be selected for 
    this operation to succeed.

    This command operates on a disk that is in SAN offline mode.
    
    If the disk is dynamic, it is both read only and offline, and, the 
    desired state is read\write and online, the suggested order of 
    operations is to first make the disk read\write, and then bring 
    the disk online. If a dynamic read only disk is brought online, it's
    status will be 'Errors'. The reason for this is that when a dynamic
    disk is brought online, the volume manager must write to the Dynamic
    Disk Database on the disk to update it's state. These writes will 
    fail if the dynamic disk is read only.

Examples:

    ONLINE DISK