Since then the rebuild / equalize technology has changed! Well, not for existing systems, but the new VNX family aka VNX2 does things a bit differently.
In the old days when a drive failed, a suitable Hot spare would kick in and the unprotected LUNs (regarding the failed drive) would be rebuild onto the Hot Spare. After a while, when the rebuild was done and the failed drive was replaced by a replacement drive, the data on the Hot spare would need to be copied to that new drive. This was called equalizing.
In the VNX2 (with MCx) this last step doesn’t exist anymore. So that means the Hot spare that was used to contain the rebuilt data is not longer a Hot Spare! It has become a regular drive! And that replacement drive will now be a new Hot Spare. When configuring a new VNX2 you’d see rules about Hot Spares and you simply don’t even need to configure Hot Spares anymore. Just make sure you have some unconfigured drives and you’re good. Your VNX2 will make sure they’re used as Hot Spares from then on.
If I remember correctly the DMX4 had a similar feature back in 2008, but it now flowed to the midrange platform as well.