A system garbage collection method and a method for collecting garbage in a solid state hard disk. A system controller determines a first logical block group to be collected, the first logical block group comprises a first data logical block, the first data logical block is located in a first solid state hard disk among a plurality of solid state hard disks, valid data is stored in a first logical address in the first logical block group, and the first logical address has a correlation with an actual address where the valid data is stored in the plurality of solid state hard disks. The system controller creates a second logical block group, and at least one second data logical block in the second logical block group is distributed on the solid state hard disk where the first data logical block storing valid data is located, thereby ensuring that the valid data migrates from the first logical block group to the second logical block group while the actual address thereof remains unchanged so as to reduce write amplification.
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