diff --git a/Cargo.lock b/Cargo.lock
index a7cbc1019..664b9fec4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1074,6 +1074,7 @@ version = "0.0.0"
 dependencies = [
  "async-trait",
  "buf_channel",
+ "bytes",
  "common",
  "config",
  "error",
diff --git a/cas/store/BUILD b/cas/store/BUILD
index 1d0e49527..aa85a29c8 100644
--- a/cas/store/BUILD
+++ b/cas/store/BUILD
@@ -157,6 +157,7 @@ rust_library(
         "//util:common",
         "//util:error",
         "//util:metrics_utils",
+        "@crate_index//:bytes",
         "@crate_index//:futures",
     ],
 )
diff --git a/cas/store/fast_slow_store.rs b/cas/store/fast_slow_store.rs
index aaf668999..b40f001e5 100644
--- a/cas/store/fast_slow_store.rs
+++ b/cas/store/fast_slow_store.rs
@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::cmp::{max, min};
+use std::ops::Range;
 use std::pin::Pin;
 use std::sync::Arc;
 
@@ -81,6 +83,26 @@ impl FastSlowStore {
     fn pin_slow_store(&self) -> Pin<&dyn StoreTrait> {
         Pin::new(self.slow_store.as_ref())
     }
+
+    /// Returns the range of bytes that should be sent given a slice bounds
+    /// offset so the output range maps the received_range.start to 0.
+    // TODO(allada) This should be put into utils, as this logic is used
+    // elsewhere in the code.
+    pub fn calculate_range(received_range: &Range<usize>, send_range: &Range<usize>) -> Option<Range<usize>> {
+        // Protect against subtraction overflow.
+        if received_range.start >= received_range.end {
+            return None;
+        }
+
+        let start = max(received_range.start, send_range.start);
+        let end = min(received_range.end, send_range.end);
+        if received_range.contains(&start) && received_range.contains(&(end - 1)) {
+            // Offset both to the start of the received_range.
+            Some(start - received_range.start..end - received_range.start)
+        } else {
+            None
+        }
+    }
 }
 
 #[async_trait]
@@ -181,21 +203,21 @@ impl StoreTrait for FastSlowStore {
         if fast_store.has(digest).await?.is_some() {
             return fast_store.get_part(digest, writer, offset, length).await;
         }
-        // We can only copy the data to our fast store if we are copying everything.
-        if offset != 0 || length.is_some() {
-            return slow_store.get_part(digest, writer, offset, length).await;
-        }
 
-        let sz_result = slow_store
+        let sz = slow_store
             .has(digest)
             .await
-            .err_tip(|| "Failed to run has() on slow store")?;
-        let Some(sz) = sz_result else {
-            return Err(make_err!(
-                Code::NotFound,
-                "Object not found in either fast or slow store"
-            ));
-        };
+            .err_tip(|| "Failed to run has() on slow store")?
+            .ok_or_else(|| {
+                make_err!(
+                    Code::NotFound,
+                    "Object {} not found in either fast or slow store",
+                    digest.hash_str()
+                )
+            })?;
+
+        let send_range = offset..length.map_or(usize::MAX, |length| length + offset);
+        let mut bytes_received: usize = 0;
 
         let (mut fast_tx, fast_rx) = make_buf_channel_pair();
         let (slow_tx, mut slow_rx) = make_buf_channel_pair();
@@ -212,20 +234,22 @@ impl StoreTrait for FastSlowStore {
                     // all the data they wanted, which could lead to an error when writing this
                     // EOF. If that was to happen, we could end up terminating this early and
                     // the resulting upload to the fast store might fail.
-                    let _ = fast_tx.send_eof().await?;
-                    let _ = writer_pin.send_eof().await?;
-                    return Ok(());
-                }
-                let (fast_tx_res, writer_res) = join!(
-                    fast_tx.send(output_buf.clone()).boxed(),
-                    writer_pin.send(output_buf).boxed(),
-                );
-                if let Err(err) = fast_tx_res {
-                    return Err(err).err_tip(|| "Failed to write to fast store in fast_slow store");
-                }
-                if let Err(err) = writer_res {
-                    return Err(err).err_tip(|| "Failed to write result to writer in fast_slow store");
+                    let (fast_res, slow_res) = join!(fast_tx.send_eof(), writer_pin.send_eof());
+                    return fast_res.merge(slow_res);
                 }
+
+                let writer_fut = if let Some(range) =
+                    Self::calculate_range(&(bytes_received..bytes_received + output_buf.len()), &send_range)
+                {
+                    writer_pin.send(output_buf.slice(range)).right_future()
+                } else {
+                    futures::future::ready(Ok(())).left_future()
+                };
+                bytes_received += output_buf.len();
+
+                let (fast_tx_res, writer_res) = join!(fast_tx.send(output_buf), writer_fut);
+                fast_tx_res.err_tip(|| "Failed to write to fast store in fast_slow store")?;
+                writer_res.err_tip(|| "Failed to write result to writer in fast_slow store")?;
             }
         };
 
diff --git a/cas/store/filesystem_store.rs b/cas/store/filesystem_store.rs
index b41f0b87c..3ebc299f9 100644
--- a/cas/store/filesystem_store.rs
+++ b/cas/store/filesystem_store.rs
@@ -482,7 +482,7 @@ impl<Fe: FileEntry> FilesystemStore<Fe> {
         self.evicting_map
             .get(digest)
             .await
-            .ok_or_else(|| make_err!(Code::NotFound, "not found in filesystem store"))
+            .ok_or_else(|| make_err!(Code::NotFound, "{} not found in filesystem store", digest.hash_str()))
     }
 
     async fn update_file<'a>(
@@ -637,7 +637,7 @@ impl<Fe: FileEntry> StoreTrait for FilesystemStore<Fe> {
             .evicting_map
             .get(&digest)
             .await
-            .ok_or_else(|| make_err!(Code::NotFound, "not found in filesystem store"))?;
+            .ok_or_else(|| make_err!(Code::NotFound, "{} not found in filesystem store", digest.hash_str()))?;
         let read_limit = length.unwrap_or(usize::MAX) as u64;
         let mut resumeable_temp_file = entry.read_file_part(offset as u64, read_limit).await?;
 
diff --git a/cas/store/tests/fast_slow_store_test.rs b/cas/store/tests/fast_slow_store_test.rs
index de91b20ac..e31bdeb2b 100644
--- a/cas/store/tests/fast_slow_store_test.rs
+++ b/cas/store/tests/fast_slow_store_test.rs
@@ -116,7 +116,7 @@ mod fast_slow_store_tests {
     }
 
     #[tokio::test]
-    async fn partial_reads_do_not_copy_to_slow_store_test() -> Result<(), Error> {
+    async fn partial_reads_copy_full_to_fast_store_test() -> Result<(), Error> {
         let (fast_slow_store, fast_store, slow_store) = make_stores();
         let fast_slow_store = Pin::new(fast_slow_store.as_ref());
         let fast_store = Pin::new(fast_store.as_ref());
@@ -127,13 +127,91 @@ mod fast_slow_store_tests {
         slow_store.update_oneshot(digest, original_data.clone().into()).await?;
 
         // This get() request should place the data in fast_store too.
-        fast_slow_store.get_part_unchunked(digest, 0, Some(50), None).await?;
+        assert_eq!(
+            original_data[10..60],
+            fast_slow_store.get_part_unchunked(digest, 10, Some(50), None).await?
+        );
 
-        // Data should not exist in fast store, but should exist in slow store because
-        // it was a partial read.
-        assert_eq!(fast_store.has(digest).await, Ok(None));
+        // Full data should exist in the fast store even though only partially
+        // read.
         check_data(slow_store, digest, &original_data, "slow_store").await?;
+        check_data(fast_store, digest, &original_data, "fast_store").await?;
 
         Ok(())
     }
+
+    #[test]
+    fn calculate_range_test() {
+        let test = |start_range, end_range| FastSlowStore::calculate_range(&start_range, &end_range);
+        {
+            // Exact match.
+            let received_range = 0..1;
+            let send_range = 0..1;
+            let expected_results = Some(0..1);
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+        {
+            // Minus one on received_range.
+            let received_range = 1..4;
+            let send_range = 1..5;
+            let expected_results = Some(0..3);
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+        {
+            // Minus one on send_range.
+            let received_range = 1..5;
+            let send_range = 1..4;
+            let expected_results = Some(0..3);
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+        {
+            // Should have already sent all data (start fence post).
+            let received_range = 1..2;
+            let send_range = 0..1;
+            let expected_results = None;
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+        {
+            // Definiltly already sent data.
+            let received_range = 2..3;
+            let send_range = 0..1;
+            let expected_results = None;
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+        {
+            // All data should be sent (inside range).
+            let received_range = 3..4;
+            let send_range = 0..100;
+            let expected_results = Some(0..1); // Note: This is relative received_range.start.
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+        {
+            // Subset of received data should be sent.
+            let received_range = 1..100;
+            let send_range = 3..4;
+            let expected_results = Some(2..3); // Note: This is relative received_range.start.
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+        {
+            // We are clearly not at the offset yet.
+            let received_range = 0..1;
+            let send_range = 3..4;
+            let expected_results = None;
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+        {
+            // Not at offset yet (fence post).
+            let received_range = 0..1;
+            let send_range = 1..2;
+            let expected_results = None;
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+        {
+            // Head part of the received data should be sent.
+            let received_range = 1..3;
+            let send_range = 2..5;
+            let expected_results = Some(1..2);
+            assert_eq!(test(received_range, send_range), expected_results);
+        }
+    }
 }
diff --git a/cas/worker/local_worker.rs b/cas/worker/local_worker.rs
index d037e6741..1812193b5 100644
--- a/cas/worker/local_worker.rs
+++ b/cas/worker/local_worker.rs
@@ -280,6 +280,9 @@ impl<'a, T: WorkerApiClientTrait, U: RunningActionsManager> LocalWorkerImpl<'a,
                             futures.push(
                                 tokio::spawn(start_action_fut).map(move |res| {
                                     let res = res.err_tip(|| "Failed to launch spawn")?;
+                                    if let Err(err) = &res {
+                                        log::info!("\x1b[0;31mError executing action\x1b[0m: {}", err);
+                                    }
                                     add_future_channel
                                         .send(make_publish_future(res).boxed())
                                         .map_err(|_| make_err!(Code::Internal, "LocalWorker could not send future"))?;
diff --git a/cas/worker/running_actions_manager.rs b/cas/worker/running_actions_manager.rs
index 32b6db3b2..67bdda254 100644
--- a/cas/worker/running_actions_manager.rs
+++ b/cas/worker/running_actions_manager.rs
@@ -894,6 +894,15 @@ impl RunningActionImpl {
         let mut output_directory_symlinks = vec![];
         let mut output_file_symlinks = vec![];
 
+        if execution_result.exit_code != 0 {
+            log::info!(
+                "Command returned exit code {} : {} {}",
+                execution_result.exit_code,
+                std::str::from_utf8(&execution_result.stdout).unwrap_or(""),
+                std::str::from_utf8(&execution_result.stderr).unwrap_or("")
+            );
+        }
+
         let stdout_digest_fut = self.metrics().upload_stdout.wrap(async {
             let cursor = Cursor::new(execution_result.stdout);
             let (digest, mut cursor) = compute_digest(cursor).await?;
diff --git a/gencargo/fast_slow_store/Cargo.toml b/gencargo/fast_slow_store/Cargo.toml
index 86c21f60d..39344530d 100644
--- a/gencargo/fast_slow_store/Cargo.toml
+++ b/gencargo/fast_slow_store/Cargo.toml
@@ -20,6 +20,7 @@ doctest = false
 
 [dependencies]
 async-trait = { workspace = true }
+bytes = { workspace = true }
 futures = { workspace = true }
 
 # Local libraries.