What is the test for deliberate indifference in the context of the Eighth Amendment violation?

at 835. Even civil recklessness (failure to act in the face of an unjustifiably high risk of harm which is so obvious that it should be known) is insufficient to establish an Eighth Amendment violation. Id. at 836-37. It not enough that a reasonable person would have known of the risk or that a defendant should have known of the risk. Id. at 842. Rather, deliberate indifference is established only where the defendant subjectively "knows of and disregards an excessive risk to inmate health and safety." Toguchi v. Chung, 391 F.3d 1051, 1057 (9th Cir. 2004) (internal citation omitted) (emphasis added).