Shingled Magnetic Recording (SMR) is a data storage technology used in high-capacity hard disk drives. It writes data tracks that partially overlap each other, similar to roof shingles, which significantly increases aerial density. Because writing to one track affects adjacent ones, modifying data requires reading and rewriting entire blocks, making SMR drives slower for random write operations compared to conventional magnetic recording.
Don't put an SMR drive in the RAID array, or the rebuild times will take weeks.
SMR drives are excellent for cheap, cold-storage archives but perform terribly in NAS environments where continuous random writes occur.