In a multi-tiered system, a read temperature classification and write temperature classification per virtual block (VLB) can be determined based on the content referenced by each VLB. The temperature classifications of VLBs can be determined using temperature scales which map read and write activity levels to corresponding temperature classifications. The temperature scales can have classification boundaries adjusted based on feedback of operations performed including down-tiering, garbage collection, and compaction and appending. In one use case, a number of free blocks in a high-performance first tier can be below a minimum and processing can be performed to locate a source block of the first tier partially filled with hot content, store the hot content contiguously on a target block of the first tier, flush write data from a log, and store the write data on the target block by appending the write data to the existing hot content.