Storage apparatus and method of controlling storage apparatus

A method of controlling a storage apparatus communicatively coupled to a server apparatus on which a plurality of applications run, the method comprising steps of:

• providing the server apparatus with a virtual volume in thin provisioning;
• performing I/O processing on the virtual volume according to an I/O request sent from the server apparatus;
• allocating, from a storage pool that is able to provide a plurality of types of physical pages classified into tiers, a physical page to each of pool pages, the pool page being an allocation unit of a storage area to the virtual volume;
• storing an I/O count of each of the pool pages, the I/O count indicating a number of the I/O requests issued to each of the pool pages;
• storing an I/O count policy that is a policy specifying a method of counting the I/O count, the I/O count policy being set for each of the applications;
• receiving information specifying the application that issued the I/O request, when receiving the I/O request;
• counting the I/O count of each of the pool pages in accordance with the I/O policy set for the application specified from the received information;
• and
• determining a tier of the physical page to be allocated to each of the pool pages, according to the I/O count of each of the pool pages, and allocating the physical page in the tier determined for each of the pool pages, to each of the pool pages.