diff --git a/pageserver/src/virtual_file.rs b/pageserver/src/virtual_file.rs
index f21b2bae15..40e0e97b0c 100644
--- a/pageserver/src/virtual_file.rs
+++ b/pageserver/src/virtual_file.rs
@@ -1295,14 +1295,14 @@ impl Drop for VirtualFileInner {
 }
 
 impl OwnedAsyncWriter for VirtualFile {
-    #[inline(always)]
-    async fn write_all<Buf: IoBuf + Send>(
-        &mut self,
+    async fn write_all_at<Buf: IoBuf + Send>(
+        &self,
         buf: FullSlice<Buf>,
+        offset: u64,
         ctx: &RequestContext,
-    ) -> std::io::Result<(usize, FullSlice<Buf>)> {
-        let (buf, res) = VirtualFile::write_all(self, buf, ctx).await;
-        res.map(move |v| (v, buf))
+    ) -> std::io::Result<FullSlice<Buf>> {
+        let (buf, res) = VirtualFile::write_all_at(self, buf, offset, ctx).await;
+        res.map(|_| buf)
     }
 }
 
@@ -1560,6 +1560,7 @@ mod tests {
             &ctx,
         )
         .await?;
+
         file_a
             .write_all(b"foobar".to_vec().slice_len(), &ctx)
             .await?;
diff --git a/pageserver/src/virtual_file/owned_buffers_io/write.rs b/pageserver/src/virtual_file/owned_buffers_io/write.rs
index c4fb209dd9..44f40bf846 100644
--- a/pageserver/src/virtual_file/owned_buffers_io/write.rs
+++ b/pageserver/src/virtual_file/owned_buffers_io/write.rs
@@ -8,11 +8,12 @@ use super::io_buf_ext::{FullSlice, IoBufExt};
 /// A trait for doing owned-buffer write IO.
 /// Think [`tokio::io::AsyncWrite`] but with owned buffers.
 pub trait OwnedAsyncWriter {
-    async fn write_all<Buf: IoBuf + Send>(
-        &mut self,
+    async fn write_all_at<Buf: IoBuf + Send>(
+        &self,
         buf: FullSlice<Buf>,
+        offset: u64,
         ctx: &RequestContext,
-    ) -> std::io::Result<(usize, FullSlice<Buf>)>;
+    ) -> std::io::Result<FullSlice<Buf>>;
 }
 
 /// A wrapper aorund an [`OwnedAsyncWriter`] that uses a [`Buffer`] to batch
@@ -109,13 +110,12 @@ where
                     .pending(),
                 0
             );
-            let (nwritten, chunk) = self
+            let chunk = self
                 .writer
-                .write_all(FullSlice::must_new(chunk), ctx)
+                .write_all_at(FullSlice::must_new(chunk), self.bytes_amount, ctx)
                 .await?;
-            self.bytes_amount += u64::try_from(nwritten).unwrap();
-            assert_eq!(nwritten, chunk_len);
-            return Ok((nwritten, chunk));
+            self.bytes_amount += u64::try_from(chunk_len).unwrap();
+            return Ok((chunk_len, chunk));
         }
         // in-memory copy the < BUFFER_SIZED tail of the chunk
         assert!(chunk.len() < self.buf().cap());
@@ -170,9 +170,11 @@ where
             return Ok(());
         }
         let slice = buf.flush();
-        let (nwritten, slice) = self.writer.write_all(slice, ctx).await?;
-        self.bytes_amount += u64::try_from(nwritten).unwrap();
-        assert_eq!(nwritten, buf_len);
+        let slice = self
+            .writer
+            .write_all_at(slice, self.bytes_amount, ctx)
+            .await?;
+        self.bytes_amount += u64::try_from(buf_len).unwrap();
         self.buf = Some(Buffer::reuse_after_flush(
             slice.into_raw_slice().into_inner(),
         ));
@@ -231,19 +233,10 @@ impl Buffer for BytesMut {
     }
 }
 
-impl OwnedAsyncWriter for Vec<u8> {
-    async fn write_all<Buf: IoBuf + Send>(
-        &mut self,
-        buf: FullSlice<Buf>,
-        _: &RequestContext,
-    ) -> std::io::Result<(usize, FullSlice<Buf>)> {
-        self.extend_from_slice(&buf[..]);
-        Ok((buf.len(), buf))
-    }
-}
-
 #[cfg(test)]
 mod tests {
+    use std::sync::Mutex;
+
     use bytes::BytesMut;
 
     use super::*;
@@ -252,16 +245,34 @@ mod tests {
 
     #[derive(Default)]
     struct RecorderWriter {
-        writes: Vec<Vec<u8>>,
+        /// record bytes and write offsets.
+        writes: Mutex<Vec<(Vec<u8>, u64)>>,
     }
+
+    impl RecorderWriter {
+        /// Gets recorded bytes and write offsets.
+        fn get_writes(&self) -> Vec<Vec<u8>> {
+            self.writes
+                .lock()
+                .unwrap()
+                .iter()
+                .map(|(buf, _)| buf.clone())
+                .collect()
+        }
+    }
+
     impl OwnedAsyncWriter for RecorderWriter {
-        async fn write_all<Buf: IoBuf + Send>(
-            &mut self,
+        async fn write_all_at<Buf: IoBuf + Send>(
+            &self,
             buf: FullSlice<Buf>,
+            offset: u64,
             _: &RequestContext,
-        ) -> std::io::Result<(usize, FullSlice<Buf>)> {
-            self.writes.push(Vec::from(&buf[..]));
-            Ok((buf.len(), buf))
+        ) -> std::io::Result<FullSlice<Buf>> {
+            self.writes
+                .lock()
+                .unwrap()
+                .push((Vec::from(&buf[..]), offset));
+            Ok(buf)
         }
     }
 
@@ -288,7 +299,7 @@ mod tests {
         write!(writer, b"e");
         let (_, recorder) = writer.flush_and_into_inner(&test_ctx()).await?;
         assert_eq!(
-            recorder.writes,
+            recorder.get_writes(),
             vec![Vec::from(b"ab"), Vec::from(b"cd"), Vec::from(b"e")]
         );
         Ok(())
@@ -304,7 +315,7 @@ mod tests {
         write!(writer, b"fghijk");
         let (_, recorder) = writer.flush_and_into_inner(&test_ctx()).await?;
         assert_eq!(
-            recorder.writes,
+            recorder.get_writes(),
             vec![Vec::from(b"abc"), Vec::from(b"de"), Vec::from(b"fghijk")]
         );
         Ok(())
@@ -320,7 +331,7 @@ mod tests {
         write!(writer, b"e");
         let (_, recorder) = writer.flush_and_into_inner(&test_ctx()).await?;
         assert_eq!(
-            recorder.writes,
+            recorder.get_writes(),
             vec![Vec::from(b"a"), Vec::from(b"bc"), Vec::from(b"de")]
         );
         Ok(())
@@ -343,7 +354,7 @@ mod tests {
 
         let (_, recorder) = writer.flush_and_into_inner(ctx).await?;
         assert_eq!(
-            recorder.writes,
+            recorder.get_writes(),
             {
                 let expect: &[&[u8]] = &[b"ab", b"cd", b"ef", b"gh", b"ij", b"kl", b"mn", b"o"];
                 expect