Any impact for non zeroed spare disk

No impact.

Drives do not need zeroing in order for a reconstruct to start. Reconstruction will overwrite the blocks on the disk, so pre-zeroing is not needed. When reconstruction starts, the spare disks label area will be erased; however, this takes only an insignificant amount of time and hence can be neglected. The same is true for Sick Disk Copy (SDC) that will copy the entire content of the disk, which on current versions of Data ONTAP is the preferred method of disk replacement (by avoiding reconstruction).

The only case where a zeroed disk is required is when a new aggregate is being built or a new disk added to increase the size of an existing aggregate. However, in this case, zeroing will start automatically. So, the only advantage of zeroing disks is that they can be added immediately if an administrator wishes to enhance the size of the aggregate.

Note: If, due to some failure in hardware, several disks of a raid group fail and cannot be re-assimilated, for example, they are orphaned due to an out-of-date timestamp/cp count, then Data ONTAP might allocate them to the spare disk pool. If further, the affected raid group is still offline, then zeroing those disks can be counterproductive as these disks still contain data and might be valuable for data recovery purposes. Therefore pre-zeroing disks should be treated with caution and only carried out when the system is healthy.