Migrating a Seagate HDD to Native 4K Sectors on a Synology NAS
The Goal I was adding a new Seagate Exos X20 (ST20000NM007D, 20 TB) to my Synology DS1821+ running DSM 7.2.2. These drives ship from the factory in 512e mode - they physically use 4096-byte sectors but advertise 512-byte sectors for legacy OS compatibility. Since my NAS and DSM support native 4K sectors, I converted the drive to 4Kn (native 4K) before adding it to the storage pool. Why Native 4K? 512e is a compatibility shim. The drive’s physical sectors are 4096 bytes, but when the OS writes a 512-byte block, the drive must read the entire 4096-byte physical sector that contains it, modify the relevant 512 bytes, and write the full sector back - a read-modify-write cycle on every write. Native 4K eliminates this: every OS write maps directly onto a physical sector. ...