The names of disk drive SMART attributes are kind of made up (sadly)

August 16, 2022

A well known part of SMART is its system of attributes, which provide assorted information about the state of the disk drive. When we talk about SMART attributes we usually use names such as "Hardware ECC Recovered", as I did in my entry on how SMART attributes can go backward. In an ideal world, the names and meanings of SMART attributes would be standardized. In a less than ideal world, at least each disk drive would tell you the name of each attribute, similar to how x86 CPUs tell you their name. Sadly we don't live in either such world, so in practice those nice SMART attribute names are what you could call made up.

The only actual identification of SMART attributes provided by disk drives (or obtained from them) is an ID number. Deciding what that ID should be called is left up to programs reading SMART data (as is how to interpret the raw value). Because of this flexibility in the standard, disk drive makers have different views on both the proper, official names of their SMART attributes as well as how to interpret them. Some low-numbered SMART attributes have almost standard names and interpretations, but even that is somewhat variable; SMART ID 9 is commonly used for 'power on hours', but both the units and the name can vary from maker to maker.

Disk drive makers may or may not share information on SMART ID names and interpretations with people; usually it's not, except perhaps to some favoured drive drive diagnostic programs. Often, information about the meaning and names of SMART attributes must be reverse engineered from various sources, especially in the open source world. Open source programs such as smartmontools often come with an extensive database of per-model attribute names and meanings; in smartmontools' case, you probably want to update its database every so often.

As a corollary of this, names for SMART attributes aren't necessarily unique; the same name may be used for different SMART IDs across different drives. Across our collection of disk drives, "Total LBAs Written" may be any of SMART ID 233 (some but not all Intel SSDs), 241 (most brands and models of our SSDs and even some HDDs), or 246 (Crucial/Micron). Meanwhile, SMART IDs 241 and 233 have five different names across our fleet, according to smartmontools.

(SMART ID 233 is especially fun; the names are "media wearout indicator", "nand gb written tlc", "sandforce internal", "total lbas written", and "total nand writes gib". The proper interpretation of values of SMART ID 233 thus varies tremendously.)

Fortunately, NVMe is more sensible about its drive health information. The NVMe equivalent of (some) SMART attributes are standardized, with fixed meanings and no particularly obvious method for expansion.

PS: Interested parties can peruse the smartmontools drivedb.h to find all sorts of other cases.

Written on 16 August 2022.
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