diff --git a/pageserver/Cargo.toml b/pageserver/Cargo.toml
index ea81544cbe..6bd2b55951 100644
--- a/pageserver/Cargo.toml
+++ b/pageserver/Cargo.toml
@@ -88,3 +88,7 @@ harness = false
 [[bench]]
 name = "bench_walredo"
 harness = false
+
+[[bench]]
+name = "bench_disk_lookup"
+harness = false
diff --git a/pageserver/benches/bench_disk_lookup.rs b/pageserver/benches/bench_disk_lookup.rs
new file mode 100644
index 0000000000..ec0a82760d
--- /dev/null
+++ b/pageserver/benches/bench_disk_lookup.rs
@@ -0,0 +1,98 @@
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use pageserver::{tenant::{disk_btree::{DiskBtreeBuilder, DiskBtreeReader, VisitDirection}, block_io::{BlockBuf, FileBlockReader}, storage_layer::DeltaLayerWriter}, repository::Key, virtual_file::{VirtualFile, self}, page_cache};
+use rand::prelude::{SeedableRng, SliceRandom, StdRng};
+use utils::{id::{TimelineId, TenantId}, lsn::Lsn};
+use std::{io::{Read, Write}, path::PathBuf};
+use pageserver::config::PageServerConf;
+
+struct MockLayer {
+    pub path: PathBuf,
+    pub index_start_blk: u32,
+    pub index_root_blk: u32,
+}
+
+impl MockLayer {
+    fn read(&self, key: i128) -> Option<u64> {
+        // Read from disk btree
+        let file = FileBlockReader::new(VirtualFile::open(&self.path).unwrap());
+        let tree_reader = DiskBtreeReader::<_, 24>::new(
+            self.index_start_blk,
+            self.index_root_blk,
+            file,
+        );
+
+        let key: Key = Key::from_i128(key);
+        let mut key_bytes: [u8; 24] = [8u8; 24];
+        key.write_to_byte_slice(&mut key_bytes);
+
+        let mut result = None;
+        tree_reader.visit(&key_bytes, VisitDirection::Backwards, |key, value| {
+            if key == key_bytes {
+                result = Some(value);
+            }
+            return true
+        }).unwrap();
+
+        result
+    }
+}
+
+// cargo bench --bench bench_disk_lookup
+fn bench_disk_lookup(c: &mut Criterion) {
+    // TODO why go through the trouble of writing to disk if we read the index
+    // into memory always?
+
+    // TODO stack 100 disk btrees
+    let _timeline = 0;
+
+    virtual_file::init(10);
+    page_cache::init(10000);
+
+    let n_keys = 250000;
+
+    // Write to disk btree
+    let block_buf = BlockBuf::new();
+    let mut writer = DiskBtreeBuilder::<_, 24>::new(block_buf);
+    for i in 0..n_keys {
+        let key: Key = Key::from_i128(i);
+        let value: u64 = i as u64;
+
+        let mut key_bytes: [u8; 24] = [8u8; 24];
+        key.write_to_byte_slice(&mut key_bytes);
+        writer.append(&key_bytes, value).unwrap();
+    }
+    let (index_root_blk, block_buf) = writer.finish().unwrap();
+    let index_start_blk = 0; // ???
+    let path = std::env::current_dir().unwrap().join("btree.tmp");
+    let layer = MockLayer {
+        path: path.clone(),
+        index_start_blk,
+        index_root_blk,
+    };
+
+    let mut file = VirtualFile::create(&path).unwrap();
+    for buf in block_buf.blocks {
+        file.write_all(buf.as_ref()).unwrap();
+    }
+
+    // Pick queries
+    let rng = &mut StdRng::seed_from_u64(1);
+    let queries: Vec<_> = (0..n_keys).collect();
+    let queries: Vec<_> = queries.choose_multiple(rng, 100).copied().collect();
+
+    // Define and name the benchmark function
+    let mut group = c.benchmark_group("g1");
+    group.bench_function("f1", |b| {
+        b.iter(|| {
+            for q in queries.clone().into_iter() {
+                black_box({
+                    assert_eq!(layer.read(q), Some(q as u64));
+                })
+            }
+        });
+    });
+    group.finish();
+}
+
+criterion_group!(group_1, bench_disk_lookup);
+criterion_main!(group_1);
diff --git a/pageserver/src/tenant/storage_layer/delta_layer.rs b/pageserver/src/tenant/storage_layer/delta_layer.rs
index ba3ab6dd4c..9657678ae5 100644
--- a/pageserver/src/tenant/storage_layer/delta_layer.rs
+++ b/pageserver/src/tenant/storage_layer/delta_layer.rs
@@ -709,6 +709,9 @@ impl DeltaLayerWriterInner {
         // FIXME: throw an error instead?
         let path = DeltaLayer::temp_path_for(conf, timeline_id, tenant_id, key_start, &lsn_range);
 
+        // HACK
+        fs::create_dir_all(path.clone().parent().unwrap())?;
+
         let mut file = VirtualFile::create(&path)?;
         // make room for the header block
         file.seek(SeekFrom::Start(PAGE_SZ as u64))?;