diff --git a/zfs-backup.py b/zfs-backup.py
index 72dcf13..d4dc4f9 100755
--- a/zfs-backup.py
+++ b/zfs-backup.py
@@ -277,16 +277,28 @@ class ZFS:
             stdin=stream.stdout,
         )
 
-    @staticmethod
-    def scrub(pool: Pool, *, wait_for_finish: bool = True) -> None:
+    @classmethod
+    def scrub(cls, pool: Pool, *, wait_for_finish: bool = True) -> None:
         if not isinstance(pool, Pool):
             raise TypeError("Can only scrub pools.")
-        # TODO: check if scrub already in progress
-        run_command([config.ZPOOL, "scrub", pool.name])
+        if not cls._scrub_in_progress(pool):
+            run_command([config.ZPOOL, "scrub", pool.name])
         if wait_for_finish:
-            # TODO make Ctrl-c interrupt this
             run_command([config.ZPOOL, "wait", "-t", "scrub", pool.name])
-    # TODO raise error if pool is not healthy
+        if not cls._healthy(pool):
+            raise IOError(f"Pool {pool.name} is not healthy.")
+
+    @classmethod
+    def _scrub_in_progress(cls, pool: Pool) -> bool:
+        return "scrub in progress" in cls._pool_status_output(pool)
+
+    @classmethod
+    def _healthy(cls, pool: Pool) -> bool:
+        return "ONLINE" in cls._pool_status_output(pool)
+
+    @staticmethod
+    def _pool_status_output(pool):
+        return get_output_of_command([config.ZFS, "status", pool.name])
 
 
 class Disk: