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Defragmentation was indeed more important on spinning disks; I think your "to reduce random seeks" is largely correct: another way to think about it is that it
by NikolaNovak 5y ago
Defragmentation was indeed more important on spinning disks; I think your "to reduce random seeks" is largely correct: another way to think about it is that it was ensuring sequential reads ("read in this 10MB file") did not become random seeks ("Sure, but that 10MB file is in these 5,381 chunks all over the place")
You are correct that SSDs do not require defragmentation, and to a certain degree defragmentation is somewhat harmful in the sense that it forces unnecessary read/write cycles.
- nayuki 5y agoIf I understand correctly, NTFS describes a file as a sequence of cluster ranges, e.g. [7,12), [0,4), [20,25). So the more fragments a file or folder has, the more space is required to describe how it's stored. This applies to the file system and is independent of HDD/SSD technology. As for SSDs, they need some degree of garbage collection - it's considered bad for an erasable block (e.g. 1 MiB) to contain a mix of live pages and deleted pages (4 KiB each).