How can you reverse the effects of an ALTER DISKGROUP … DROP DISK command if it
has already completed?
A.
Issue the ALTER DISKGROUP … ADD DISK command.
B.
Issue the ALTER DISKGROUP … UNDROP DISKS command.
C.
Issue the ALTER DISKGROUP … DROP DISK CANCEL command.
D.
Retrieve the disk from the Recycle Bin after the operation completes.
Explanation:
You cannot UNDROP DISKS if the DROP DISK command has already completed.
I am not agree
https://docs.oracle.com/cd/B28359_01/server.111/b31107/asmdiskgrps.htm#CHDFJADJ
Undropping Disks in Disk Groups
The UNDROP DISKS clause of the ALTER DISKGROUP statement enables you to cancel all pending drops of disks within disk groups. If a drop disk operation has already completed, then this statement cannot be used to restore it. This statement cannot be used to restore disks that are being dropped as the result of a DROP DISKGROUP statement, or for disks that are being dropped using the FORCE clause.
Example: Undropping Disks in Disk Groups
The following example cancels the dropping of disks from disk group dgroup1:
ALTER DISKGROUP dgroup1 UNDROP DISKS;
Excusme, option A is valid.
The key point is “… it has already COMPLETED”.
You are not allow to undrop a disk if the operation is completed.
Answer A is correct.
Option A is correct as the Disk is already dropped. It can’t be undropped.
Its a tricky question. Point here is ‘drop’ is already completed.
Answer A is correct.
“reverse the effects” is the ambiguous part of the question.