Hard Drives: Difference between revisions
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== SMR == | == SMR == | ||
Shingled Magnetic Recording (SMR) drives writes tracks that partially overlap to increase the number of tracks per platter. Writes to SMR will | '''Shingled Magnetic Recording''' ('''SMR''') drives writes tracks that partially overlap to increase the number of tracks per platter. Writes to SMR will requires the firmware to determine if adjacent tracks need rewriting. If the adjacent track contains valid data, it must also be rewritten. This process repeats for every subsequent track and causes an 'avalanche' of rewrites and results 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 tracks (using perpendicular recording) on '''Conventional Magnetic Recording''' ('''CMR''') drives. | ||
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. | 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. | ||
Revision as of 18:17, 15 April 2020
SMR
Shingled Magnetic Recording (SMR) drives writes tracks that partially overlap to increase the number of tracks per platter. Writes to SMR will requires the firmware to determine if adjacent tracks need rewriting. If the adjacent track contains valid data, it must also be rewritten. This process repeats for every subsequent track and causes an 'avalanche' of rewrites and results 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 tracks (using perpendicular recording) on Conventional Magnetic Recording (CMR) drives.
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/).
DM-SMR or SMR drives can be detected if smartctl reports the drive supporting the TRIM function. (https://github.com/openzfs/zfs/issues/10182)
Manufacturers
See: https://en.wikipedia.org/wiki/List_of_defunct_hard_disk_manufacturers
The major players now are: Seagate, Western Digital, and Toshiba.