It is an EMC solution for cloning production data.

1.Define a device as a BCV using Symmetrix Manager.2.Establish a new pair relationship between an STD device and theBCV device. Once the BCV is established as a replica of thestandard device, it is not accessible through its original deviceaddress.3.Split the BCV device from the standard device with which it waspreviously paired. After a split, the BCV device has valid dataand is available for backup or other host processes through itsoriginal device address

When sink occurs,at that time if some activity is going on the std device than?

As your post title states, this is an EMC solution (as you're using BCV volumes) - so if you want to know the exact process/underlying steps that occur during sync, you should follow up with EMC, as they are the vendor for this product.

Although you can use Symantec products (eg: Volume Manager, etc) to manage the volumes at higher level(s), the underlying sync for the BCV is controlled at the EMC level, so you need to log a case with them.

Where to ask this post?

You need to log a support case with EMC, or you could see if there are EMC communities/forums relating to this product. The point is if you're using an EMC solution and want to know more details about it, you need to ask the vendor/supplier of that solution!

As a hint, try searching in google and restricting results with site:emc.com