Impact on mirror:
A chkdsk on a volume with a mirror attached does not have impact on the mirror. There is no need to break the mirror when running a chkdsk.

Chkdsk in readonly mode:
A chkdsk in readonly mode does not exclusively lock the volume and does not impact the availability of the volume.

Chkdsk not in readonly mode:
A chkdsk that is not in readonly mode like chkdsk /f or chkdsk /x will exclusively lock the volume and will cause an "access denied " when accessing the volume during the chkdsk process.