T2 Translator workings

[Swiftdata]

Some info on the T2 translator in new WD SMR drives.

Shingled Magnetic Recording (SMR) technology increases areal density by allowing more tracks to be written per platter surface. This is accomplished by designing the read element of the head assembly to be significantly narrower than the write element. As each track is written, the subsequent track partially overlaps it, offset by the width of the read element. This overlapping pattern resembles roof shingles, which gives the technology its name.

Management of this recording method relies on a secondary translation layer. Because the write head is wider than an individual accessible track, modifying a single sector requires rewriting not only the affected track but also any immediately adjacent tracks that follow it. To ensure data integrity, the contents of all impacted tracks must be read, preserved, and rewritten as part of the update process.

This operation is time-consuming and has a substantial impact on performance. To mitigate this, updates to individual sectors are redirected to unused tracks that do not require preservation of existing data. The physical-to-logical mapping is then updated so the logical sector address points to a new physical location. The second level translation system maintains these mappings, allowing the logical addressing scheme to remain consistent despite physical relocation of data.

Physical tracks containing obsolete versions of data are typically cleared using processes such as TRIM, which usually run during idle periods to minimize performance impact. Until these tracks are erased, previous data versions remain physically present and may be recoverable.

By analyzing these retained versions, it may be possible to recover deleted data, or restore user data lost after a partition format.