Storage device and operating method of storage controller

A storage device, comprising:

• a non-volatile memory comprising a plurality of memory stacks that are independently erasable, each memory stack of the plurality of memory stacks extending in a vertical direction on a substrate;
• and
• a storage controller comprising a processor configured to control a garbage collection operation on the plurality of memory stacks,
• wherein the plurality of memory stacks comprises:
• a plurality of first memory stacks arranged on the substrate, each first memory stack of the plurality of first memory stacks being coupled to a first word line group and having a first size, the first word line group comprising a plurality of first word lines stacked in the vertical direction;
• and
• a plurality of second memory stacks arranged on the plurality of first memory stacks, each second memory stack of the plurality of second memory stacks being coupled to a second word line group and having a second size, the second size being different from the first size, the second word line group comprising a plurality of second word lines stacked in the vertical direction, and
• wherein the processor is further configured to:
• select a victim memory stack with a lowest ratio of a valid page count to an invalid page count from among the plurality of memory stacks;
• and
• copy a valid page of the victim memory stack to a target memory stack from among the plurality of memory stacks.

An operating method of a processor of a storage device, the operating method comprising:

• selecting a victim memory stack from among first memory stacks and second memory stacks of a non-volatile memory, the first memory stacks being on a substrate, the second memory stacks being on the first memory stacks, each of the first memory stacks having a first size, each of the second memory stacks having a second size, the second size being different from the first size;
• copying a valid page of the victim memory stack to a target memory stack;
• and
• performing an erase operation on the victim memory stack,
• wherein the selecting of the victim memory stack comprises at least one of:
• selecting, as the victim memory stack, a first memory stack having a smallest ratio value of a valid page count to an invalid page count from among the first memory stacks and the second memory stacks;
• selecting, as the victim memory stack, a second memory stack having a largest difference value between the invalid page count and the valid page count from among the first memory stacks and the second memory stacks;
• or
• selecting, as the victim memory stack, a third memory stack having a smallest ratio value of the valid page count to a block size from among the first memory stacks and the second memory stacks.