Conventional Magnetic Recording

Overview

Conventional Magnetic Recording (CMR) is the traditional HDD recording technology where sectors are all equally and randomly writable. This random-write model is what makes data-safe regeneration hard: current depopulation on CMR drives requires a full reformat via Remove Element and Truncate, destroying all existing data. Because many data center providers remain all-CMR, Seagate is researching how to extend zone-style depopulation to conventional drives without a full reformat.

Two of the proposed CMR approaches were detailed at OCP Global Summit 2025. Solution 1, CMR Zones, adds a zone-reporting structure to standard CMR HDDs using 256 MB zones aligned to head boundaries; it keeps data online and prevents rebuilds for 95% of capacity but introduces approximately 7% average LBA loss from zone collateral damage. Solution 2 uses the LBA Status Log for host-managed relocation: average LBA loss drops to about 5% with minimized collateral damage, but it can generate millions of remap entries that challenge host management at scale. (A third approach, drive-managed Optimized Provisioning, is covered as its own concept.)