diff --git a/core/file.hh b/core/file.hh
index 66966e291d..e1ab3649ad 100644
--- a/core/file.hh
+++ b/core/file.hh
@@ -62,6 +62,7 @@ public:
     virtual future<struct stat> stat(void) = 0;
     virtual future<> truncate(uint64_t length) = 0;
     virtual future<> discard(uint64_t offset, uint64_t length) = 0;
+    virtual future<> allocate(uint64_t position, uint64_t length) = 0;
     virtual future<size_t> size(void) = 0;
     virtual subscription<directory_entry> list_directory(std::function<future<> (directory_entry de)> next) = 0;
 
@@ -86,6 +87,7 @@ public:
     future<struct stat> stat(void);
     future<> truncate(uint64_t length);
     future<> discard(uint64_t offset, uint64_t length);
+    virtual future<> allocate(uint64_t position, uint64_t length) override;
     future<size_t> size(void);
     virtual subscription<directory_entry> list_directory(std::function<future<> (directory_entry de)> next) override;
 };
@@ -96,6 +98,7 @@ public:
     future<> truncate(uint64_t length) override;
     future<> discard(uint64_t offset, uint64_t length) override;
     future<size_t> size(void) override;
+    virtual future<> allocate(uint64_t position, uint64_t length) override;
 };
 
 inline
@@ -228,6 +231,22 @@ public:
         return _file_impl->truncate(length);
     }
 
+    /// Preallocate disk blocks for a specified byte range.
+    ///
+    /// Requests the file system to allocate disk blocks to
+    /// back the specified range (\c length bytes starting at
+    /// \c position).  The range may be outside the current file
+    /// size; the blocks can then be used when appending to the
+    /// file.
+    ///
+    /// \param position beginning of the range at which to allocate
+    ///                 blocks.
+    /// \parm length length of range to allocate.
+    /// \return future that becomes ready when the operation completes.
+    future<> allocate(uint64_t position, uint64_t length) {
+        return _file_impl->allocate(position, length);
+    }
+
     future<> discard(uint64_t offset, uint64_t length) {
         return _file_impl->discard(offset, length);
     }
diff --git a/core/fstream.cc b/core/fstream.cc
index 103e34df54..bc7b05d7c1 100644
--- a/core/fstream.cc
+++ b/core/fstream.cc
@@ -81,11 +81,12 @@ input_stream<char> make_file_input_stream(
 
 class file_data_sink_impl : public data_sink_impl {
     lw_shared_ptr<file> _file;
-    size_t _buffer_size;
+    file_output_stream_options _options;
     uint64_t _pos = 0;
+    uint64_t _last_preallocation = 0;
 public:
-    file_data_sink_impl(lw_shared_ptr<file> f, size_t buffer_size)
-            : _file(std::move(f)), _buffer_size(buffer_size) {}
+    file_data_sink_impl(lw_shared_ptr<file> f, file_output_stream_options options)
+            : _file(std::move(f)), _options(options) {}
     future<> put(net::packet data) { return make_ready_future<>(); }
     virtual temporary_buffer<char> allocate_buffer(size_t size) override {
         // buffers to dma_write must be aligned to 512 bytes.
@@ -108,12 +109,20 @@ public:
             buf_size = buf.size();
             truncate = true;
         }
-        return _file->dma_write(pos, p, buf_size).then(
-            [this, buf = std::move(buf), truncate] (size_t size) {
-            if (truncate) {
-                return _file->truncate(_pos);
-            }
-            return make_ready_future<>();
+        auto prealloc = make_ready_future<>();
+        if (pos + buf_size > _last_preallocation) {
+            auto old = _last_preallocation;
+            _last_preallocation = align_down<uint64_t>(old + _options.preallocation_size, _options.preallocation_size);
+            prealloc = _file->allocate(old, _last_preallocation - old);
+        }
+        return prealloc.then([this, pos, p, buf_size, truncate, buf = std::move(buf)] () mutable {
+            _file->dma_write(pos, p, buf_size).then(
+                    [this, buf = std::move(buf), truncate] (size_t size) {
+                if (truncate) {
+                    return _file->truncate(_pos);
+                }
+                return make_ready_future<>();
+            });
         });
     }
     future<> close() { return _file->flush(); }
@@ -121,11 +130,18 @@ public:
 
 class file_data_sink : public data_sink {
 public:
-    file_data_sink(lw_shared_ptr<file> f, size_t buffer_size)
+    file_data_sink(lw_shared_ptr<file> f, file_output_stream_options options)
         : data_sink(std::make_unique<file_data_sink_impl>(
-                std::move(f), buffer_size)) {}
+                std::move(f), options)) {}
 };
 
 output_stream<char> make_file_output_stream(lw_shared_ptr<file> f, size_t buffer_size) {
-    return output_stream<char>(file_data_sink(std::move(f), buffer_size), buffer_size);
+    file_output_stream_options options;
+    options.buffer_size = buffer_size;
+    return make_file_output_stream(std::move(f), options);
 }
+
+output_stream<char> make_file_output_stream(lw_shared_ptr<file> f, file_output_stream_options options) {
+    return output_stream<char>(file_data_sink(std::move(f), options), options.buffer_size);
+}
+
diff --git a/core/fstream.hh b/core/fstream.hh
index 8942018f56..1fd62e49a8 100644
--- a/core/fstream.hh
+++ b/core/fstream.hh
@@ -39,9 +39,22 @@ input_stream<char> make_file_input_stream(
         lw_shared_ptr<file> file, uint64_t offset = 0,
         uint64_t buffer_size = 8192);
 
+struct file_output_stream_options {
+    unsigned buffer_size = 8192;
+    unsigned preallocation_size = 1024*1024; // 1MB
+};
+
 // Create an output_stream for writing starting at the position zero of a
 // newly created file.
 // NOTE: flush() should be the last thing to be called on a file output stream.
 output_stream<char> make_file_output_stream(
         lw_shared_ptr<file> file,
         uint64_t buffer_size = 8192);
+
+/// Create an output_stream for writing starting at the position zero of a
+/// newly created file.
+/// NOTE: flush() should be the last thing to be called on a file output stream.
+output_stream<char> make_file_output_stream(
+        lw_shared_ptr<file> file,
+        file_output_stream_options options);
+
diff --git a/core/reactor.cc b/core/reactor.cc
index 8e5992a2d0..e29dd8ea4e 100644
--- a/core/reactor.cc
+++ b/core/reactor.cc
@@ -571,6 +571,26 @@ posix_file_impl::discard(uint64_t offset, uint64_t length) {
     });
 }
 
+future<>
+posix_file_impl::allocate(uint64_t position, uint64_t length) {
+    // FALLOC_FL_ZERO_RANGE is fairly new, so don't fail if it's not supported.
+    static bool supported = true;
+    if (!supported) {
+        return make_ready_future<>();
+    }
+    return engine()._thread_pool.submit<syscall_result<int>>([this, position, length] () mutable {
+        auto ret = ::fallocate(_fd, FALLOC_FL_ZERO_RANGE|FALLOC_FL_KEEP_SIZE, position, length);
+        if (ret == -1 && errno == EOPNOTSUPP) {
+            ret = 0;
+            supported = false; // Racy, but harmless.  At most we issue an extra call or two.
+        }
+        return wrap_syscall<int>(ret);
+    }).then([] (syscall_result<int> sr) {
+        sr.throw_if_error();
+        return make_ready_future<>();
+    });
+}
+
 future<>
 blockdev_file_impl::discard(uint64_t offset, uint64_t length) {
     return engine()._thread_pool.submit<syscall_result<int>>([this, offset, length] () mutable {
@@ -582,6 +602,12 @@ blockdev_file_impl::discard(uint64_t offset, uint64_t length) {
     });
 }
 
+future<>
+blockdev_file_impl::allocate(uint64_t position, uint64_t length) {
+    // nothing to do for block device
+    return make_ready_future<>();
+}
+
 future<size_t>
 posix_file_impl::size(void) {
     return posix_file_impl::stat().then([] (struct stat&& st) {