diff --git a/docs/storage.md b/docs/storage.md
index 243b46c20..d2df74039 100644
--- a/docs/storage.md
+++ b/docs/storage.md
@@ -42,12 +42,17 @@ The directory structure of a Prometheus server's data directory will look someth
     └── checkpoint.000001
 ```
 
-The initial two-hour blocks are eventually compacted into longer blocks in the background.
 
 Note that a limitation of the local storage is that it is not clustered or replicated. Thus, it is not arbitrarily scalable or durable in the face of disk or node outages and should thus be treated as more of an ephemeral sliding window of recent data. However, if your durability requirements are not strict, you may still succeed in storing up to years of data in the local storage.
 
 For further details on file format, see [TSDB format](https://github.com/prometheus/tsdb/blob/master/docs/format/README.md).
 
+## Compaction
+
+The initial two-hour blocks are eventually compacted into longer blocks in the background.
+
+Compaction will create larger blocks up to 10% of the rention time, or 21 days, whichever is smaller.
+
 ## Operational aspects
 
 Prometheus has several flags that allow configuring the local storage. The most important ones are:
@@ -70,6 +75,8 @@ If your local storage becomes corrupted for whatever reason, your best bet is to
 
 If both time and size retention policies are specified, whichever policy triggers first will be used at that instant.
 
+Expired block cleanup happens on a background schedule. It may take up to two hours remove expired blocks. Expired blocks must be fully expired before they are cleaned up.
+
 ## Remote storage integrations
 
 Prometheus's local storage is limited by single nodes in its scalability and durability. Instead of trying to solve clustered storage in Prometheus itself, Prometheus has a set of interfaces that allow integrating with remote storage systems.