Write amplification. It's been a hot minute since I really dived into specifics, but as I recall few (if any modern) SSDs are actually 512b under the hood, and writing 512b still requires a larger free area (and erase pages are even larger, but thats a whole other discussion). IIRC even many "4k native" drives need 8k or 16k free blocks to write. If you tell the OS/file system the drive is 512b, it will sometimes issue multiple 512b writes that should have been contiguous as part of (or all of) a 4k block. This will not always be automatically fixed, its an "it depends". When it isn't a 4k write can turn into 8 4k writes. In order to "save space" the file system would ALSO need to use 512b sectors/clusters/blocks. A 1TB drive with 4k sectors (drive and file system) can store close to 250 million files. If you have even close to 100 million files in most file systems on a single drive you are having what is known as "a bad time". NTFS minimum is 4K, while EXT3/4 is "clever" and you can store more than one inode per physical disk sector already (depending on format options).
512b mode is for legacy compatibility, and generally comes with downsides to iops/performance (including increased CPU overhead).
512b mode is for legacy compatibility, and generally comes with downsides to iops/performance (including increased CPU overhead).
