Depends on what kind of data is in question. Backups and old incremential data can stay encrypted while disks are otherwise in use.

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stavros 2 hours ago | parent [-]

Hm yeah, I always think of encryption at rest as "the drive handles encryption itself", rather than "we encrypted these archives before we wrote them", but fair enough.

	▲	literalAardvark 2 hours ago \| parent [-]
		Not necessarily the drive, but yeah, where standards mandate encryption at rest you need to have the files on the live disk encrypted. Usually it's much less of a headache to luks/bitlocker/SED the whole drive so that you don't have to worry about swap files and logs