Linux 4.13 DM Picks Up Support For SMR/Zoned Devices

The Device Mapper (DM) updates have been pulled into mainline Git for the Linux 4.13 merge window.

Perhaps most prominent to end-users for the Device Mapper changes in Linux 4.13 is support for zoned/SMR devices in DM core. The past few kernel releases have seen work in the area of shingled magnetic recording (SMR) devices across different areas, including native support within some file-systems.

SMR is designed to increase the storage density of hard drives and has been in use the past few years by a few manufacturers for their high capacity drives (~10 TB HDD disks). With Linux 4.13 comes a new dm-zoned target that exposes a zoned block device (ZBC/ZAC) as a regular block device that in turn hides from the user/file-system the peculiars of a zoned block device. The dm-zoned work is designed to reduce system overhead. From the new DM_ZONED Kconfig option:

This device-mapper target takes a host-managed or host-aware zoned block device and exposes most of its capacity as a regular block device (drive-managed zoned block device) without any write constraints. This is mainly intended for use with file systems that do not natively support zoned block devices but still want to benefit from the increased capacity offered by SMR disks. Other uses by applications using raw block devices (for example object stores) are also possible.

More details on the new dm-zoned can be found via the new documentation.

The DeviceMapper updates also have a RAID fix, some big endian work, and other smaller changes. More details via this Git merge.