Clarify comments

csi.proto

@@ -1328,7 +1328,10 @@ message VolumeHealth {
   option (alpha_message) = true;
 
   enum Condition {
-    // Volume health condition is unknown; treat it as healthy.
+    // Volume health condition is unknown; If this is the initial
+    // report of volume health, treat it as healthy. If there was
+    // already a condition reported previously, treat unknown as
+    // unchanged from the previous condition.
     UNKNOWN = 0;
     // Volume is accessible and no problems are detected. 
     HEALTHY = 1;
@@ -1337,13 +1340,15 @@ message VolumeHealth {
     // maintenance.
     TEMPORARY_INACCESSIBLE = 2;
     // Volume is accessible currently, but is degraded. Data loss
-    // is unlikely as the storage system is fixing the problem
-    // automatically.
+    // is unlikely as the storage system is rebuilding to fix the
+    // problem automatically. For example, a replica is lost on
+    // the storage system but a spare is configured, and the storage
+    // system is resyncing/reconstructing.
     TEMPORARY_DEGRADED = 3;
     // Volume is accessible currently, but a problem is detected that
     // could lead to eventual data loss. Examples: recoverable hardware
-    // failure, cooling failure, equipment significantly past end of
-    // life.
+    // failure (i.e. the disk needs to be manually replaced by a human),
+    // cooling failure, equipment significantly past end of life.
     FAILURE_LIKELY = 4;
     // Volume is not accessible currently, and there is reason to
     // believe the outage may be permanent. Examples: unrecoverable

spec.md

@@ -2336,7 +2336,10 @@ message VolumeHealth {
   option (alpha_message) = true;
 
   enum Condition {
-    // Volume health condition is unknown; treat it as healthy.
+    // Volume health condition is unknown; If this is the initial
+    // report of volume health, treat it as healthy. If there was
+    // already a condition reported previously, treat unknown as
+    // unchanged from the previous condition.
     UNKNOWN = 0;
     // Volume is accessible and no problems are detected. 
     HEALTHY = 1;
@@ -2345,13 +2348,15 @@ message VolumeHealth {
     // maintenance.
     TEMPORARY_INACCESSIBLE = 2;
     // Volume is accessible currently, but is degraded. Data loss
-    // is unlikely as the storage system is fixing the problem
-    // automatically.
+    // is unlikely as the storage system is rebuilding to fix the
+    // problem automatically. For example, a replica is lost on
+    // the storage system but a spare is configured, and the storage
+    // system is resyncing/reconstructing.
     TEMPORARY_DEGRADED = 3;
     // Volume is accessible currently, but a problem is detected that
     // could lead to eventual data loss. Examples: recoverable hardware
-    // failure, cooling failure, equipment significantly past end of
-    // life.
+    // failure (i.e. the disk needs to be manually replaced by a human),
+    // cooling failure, equipment significantly past end of life.
     FAILURE_LIKELY = 4;
     // Volume is not accessible currently, and there is reason to
     // believe the outage may be permanent. Examples: unrecoverable