diff --git a/block_util/src/lib.rs b/block_util/src/lib.rs
index 3d13003c9..b809243d0 100644
--- a/block_util/src/lib.rs
+++ b/block_util/src/lib.rs
@@ -25,6 +25,7 @@ use io_uring::{opcode, IoUring, Probe};
 use smallvec::SmallVec;
 use std::alloc::{alloc_zeroed, dealloc, Layout};
 use std::cmp;
+use std::collections::VecDeque;
 use std::convert::TryInto;
 use std::fs::File;
 use std::io::{self, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write};
@@ -595,7 +596,7 @@ where
         iovecs: &[libc::iovec],
         user_data: u64,
         eventfd: &EventFd,
-        completion_list: &mut Vec<(u64, i32)>,
+        completion_list: &mut VecDeque<(u64, i32)>,
     ) -> AsyncIoResult<()> {
         // Convert libc::iovec into IoSliceMut
         let mut slices = Vec::new();
@@ -616,7 +617,7 @@ where
                 .map_err(AsyncIoError::ReadVectored)?
         };
 
-        completion_list.push((user_data, result as i32));
+        completion_list.push_back((user_data, result as i32));
         eventfd.write(1).unwrap();
 
         Ok(())
@@ -628,7 +629,7 @@ where
         iovecs: &[libc::iovec],
         user_data: u64,
         eventfd: &EventFd,
-        completion_list: &mut Vec<(u64, i32)>,
+        completion_list: &mut VecDeque<(u64, i32)>,
     ) -> AsyncIoResult<()> {
         // Convert libc::iovec into IoSlice
         let mut slices = Vec::new();
@@ -649,7 +650,7 @@ where
                 .map_err(AsyncIoError::WriteVectored)?
         };
 
-        completion_list.push((user_data, result as i32));
+        completion_list.push_back((user_data, result as i32));
         eventfd.write(1).unwrap();
 
         Ok(())
@@ -659,7 +660,7 @@ where
         &mut self,
         user_data: Option<u64>,
         eventfd: &EventFd,
-        completion_list: &mut Vec<(u64, i32)>,
+        completion_list: &mut VecDeque<(u64, i32)>,
     ) -> AsyncIoResult<()> {
         let result: i32 = {
             let mut file = self.file();
@@ -671,7 +672,7 @@ where
         };
 
         if let Some(user_data) = user_data {
-            completion_list.push((user_data, result));
+            completion_list.push_back((user_data, result));
             eventfd.write(1).unwrap();
         }
 
diff --git a/block_util/src/qcow_sync.rs b/block_util/src/qcow_sync.rs
index 1202fba0b..5d9c042a7 100644
--- a/block_util/src/qcow_sync.rs
+++ b/block_util/src/qcow_sync.rs
@@ -5,6 +5,7 @@
 use crate::async_io::{AsyncIo, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult};
 use crate::AsyncAdaptor;
 use qcow::{QcowFile, RawFile, Result as QcowResult};
+use std::collections::VecDeque;
 use std::fs::File;
 use std::io::{Seek, SeekFrom};
 use std::sync::{Arc, Mutex, MutexGuard};
@@ -37,7 +38,7 @@ impl DiskFile for QcowDiskSync {
 pub struct QcowSync {
     qcow_file: Arc<Mutex<QcowFile>>,
     eventfd: EventFd,
-    completion_list: Vec<(u64, i32)>,
+    completion_list: VecDeque<(u64, i32)>,
 }
 
 impl QcowSync {
@@ -46,7 +47,7 @@ impl QcowSync {
             qcow_file,
             eventfd: EventFd::new(libc::EFD_NONBLOCK)
                 .expect("Failed creating EventFd for QcowSync"),
-            completion_list: Vec::new(),
+            completion_list: VecDeque::new(),
         }
     }
 }
@@ -98,6 +99,6 @@ impl AsyncIo for QcowSync {
     }
 
     fn next_completed_request(&mut self) -> Option<(u64, i32)> {
-        self.completion_list.pop()
+        self.completion_list.pop_front()
     }
 }
diff --git a/block_util/src/raw_sync.rs b/block_util/src/raw_sync.rs
index b9b87e0a6..b85bc14f5 100644
--- a/block_util/src/raw_sync.rs
+++ b/block_util/src/raw_sync.rs
@@ -5,6 +5,7 @@
 use crate::async_io::{
     AsyncIo, AsyncIoError, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult, DiskTopology,
 };
+use std::collections::VecDeque;
 use std::fs::File;
 use std::io::{Seek, SeekFrom};
 use std::os::unix::io::{AsRawFd, RawFd};
@@ -44,7 +45,7 @@ impl DiskFile for RawFileDiskSync {
 pub struct RawFileSync {
     fd: RawFd,
     eventfd: EventFd,
-    completion_list: Vec<(u64, i32)>,
+    completion_list: VecDeque<(u64, i32)>,
 }
 
 impl RawFileSync {
@@ -52,7 +53,7 @@ impl RawFileSync {
         RawFileSync {
             fd,
             eventfd: EventFd::new(libc::EFD_NONBLOCK).expect("Failed creating EventFd for RawFile"),
-            completion_list: Vec::new(),
+            completion_list: VecDeque::new(),
         }
     }
 }
@@ -81,7 +82,7 @@ impl AsyncIo for RawFileSync {
             return Err(AsyncIoError::ReadVectored(std::io::Error::last_os_error()));
         }
 
-        self.completion_list.push((user_data, result as i32));
+        self.completion_list.push_back((user_data, result as i32));
         self.eventfd.write(1).unwrap();
 
         Ok(())
@@ -106,7 +107,7 @@ impl AsyncIo for RawFileSync {
             return Err(AsyncIoError::WriteVectored(std::io::Error::last_os_error()));
         }
 
-        self.completion_list.push((user_data, result as i32));
+        self.completion_list.push_back((user_data, result as i32));
         self.eventfd.write(1).unwrap();
 
         Ok(())
@@ -120,7 +121,7 @@ impl AsyncIo for RawFileSync {
         }
 
         if let Some(user_data) = user_data {
-            self.completion_list.push((user_data, result));
+            self.completion_list.push_back((user_data, result));
             self.eventfd.write(1).unwrap();
         }
 
@@ -128,6 +129,6 @@ impl AsyncIo for RawFileSync {
     }
 
     fn next_completed_request(&mut self) -> Option<(u64, i32)> {
-        self.completion_list.pop()
+        self.completion_list.pop_front()
     }
 }
diff --git a/block_util/src/vhdx_sync.rs b/block_util/src/vhdx_sync.rs
index 678aedeba..a199e06e0 100644
--- a/block_util/src/vhdx_sync.rs
+++ b/block_util/src/vhdx_sync.rs
@@ -4,6 +4,7 @@
 
 use crate::async_io::{AsyncIo, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult};
 use crate::AsyncAdaptor;
+use std::collections::VecDeque;
 use std::fs::File;
 use std::sync::{Arc, Mutex, MutexGuard};
 use vhdx::vhdx::{Result as VhdxResult, Vhdx};
@@ -37,7 +38,7 @@ impl DiskFile for VhdxDiskSync {
 pub struct VhdxSync {
     vhdx_file: Arc<Mutex<Vhdx>>,
     eventfd: EventFd,
-    completion_list: Vec<(u64, i32)>,
+    completion_list: VecDeque<(u64, i32)>,
 }
 
 impl VhdxSync {
@@ -45,7 +46,7 @@ impl VhdxSync {
         Ok(VhdxSync {
             vhdx_file,
             eventfd: EventFd::new(libc::EFD_NONBLOCK)?,
-            completion_list: Vec::new(),
+            completion_list: VecDeque::new(),
         })
     }
 }
@@ -97,6 +98,6 @@ impl AsyncIo for VhdxSync {
     }
 
     fn next_completed_request(&mut self) -> Option<(u64, i32)> {
-        self.completion_list.pop()
+        self.completion_list.pop_front()
     }
 }