Hard Drives

SMR

Shingled Magnetic Recording (SMR) drives writes tracks that partially overlap to increase the number of tracks per platter. Writes to SMR will require rewriting overlapping tracks resulting in poor write performance. Drive-managed SMR (DM-SMR) drives mask the poor write performance by caching writes to a non-SMR portion of the disk and then rewriting to shingled area of the disk when idle. Read performance of SMR is equivalent to non-shingled Conventional Magnetic Recording (CMR).

When using SMR with RAID arrays or ZFS RAIDZ datasets, mixing it with non-SMR drives may cause unexpected results such as the array failing or disks being kicked out.

Western Digital Reds are DM-SMR (https://blocksandfiles.com/2020/04/14/wd-red-nas-drives-shingled-magnetic-recording/) which may cause issues in NAS applications that require high random IO. Some newer Seagate Barracuda and Desktop hard drives are also DM-SMR (https://blocksandfiles.com/2020/04/15/seagate-2-4-and-8tb-barracuda-and-desktop-hdd-smr/).