How Many Physical Hard Disks Needed in one Data Center like Google's

 The number of physical hard disks needed in a data center like Google's can vary greatly depending on a number of factors, including the size of the data center, the type and amount of data being stored, and the specific storage and redundancy requirements of the system.

However, it is safe to say that a data center the size of Google's would require an enormous number of physical hard disks to provide the necessary storage capacity and redundancy. In fact, Google uses a distributed file system called Google File System (GFS) which is designed to store and manage massive amounts of data across thousands of commodity servers and disks.

While it is difficult to provide an exact number, it is estimated that Google's data centers may contain hundreds of thousands or even millions of physical hard disks. It is worth noting, however, that Google also utilizes other forms of storage technology, such as solid-state drives (SSDs) and tape storage, to supplement their storage infrastructure.