compression algorithm of md device

Does anyone know what compression algorithm is used for md devices? I want to know that's performance, and whether it can be replaceable.

There is none.

There isn't any employed by default. But that doesn't have to stop you from compressing an md() image yourself. Which is sometimes employed when utilizing one on a CD, or DVD utility, or install disk. Or on an SSD (flash/pen drive), for that matter.

--Chris