diff --git a/pkgs/build-support/vm/default.nix b/pkgs/build-support/vm/default.nix
index e4eb993fbf1..50083ca688f 100644
--- a/pkgs/build-support/vm/default.nix
+++ b/pkgs/build-support/vm/default.nix
@@ -4,7 +4,12 @@ with pkgs;
 
 rec {
 
-  inherit (linuxPackages_2_6_32) kernel;
+  # The 15 second CIFS timeout is too short if the host if heavily
+  # loaded (e.g., in the Hydra build farm when it's running many jobs
+  # in parallel).  So apply a patch to increase the timeout to 120s.
+  kernel = pkgs.linux.override (orig: {
+    kernelPatches = orig.kernelPatches ++ [ kernelPatches.cifs_timeout ];
+  });
 
   kvm = pkgs.qemu_kvm;
 
@@ -135,10 +140,8 @@ rec {
     mkdir -p /fs/dev
     mount -o bind /dev /fs/dev
 
-    for ((n = 0; n < 10; n++)); do
-      echo "mounting host filesystem, attempt $n..."
-      mount -t cifs //10.0.2.4/qemu /fs/hostfs -o guest,username=nobody && break
-    done
+    echo "mounting host filesystem..."
+    mount -t cifs //10.0.2.4/qemu /fs/hostfs -o guest,username=nobody
 
     mkdir -p /fs/nix/store
     mount -o bind /fs/hostfs/nix/store /fs/nix/store
@@ -225,7 +228,6 @@ rec {
 
 
   startSamba =
-    let sambaScript = writeScript "run-smbd" "while ${samba}/sbin/smbd -s $TMPDIR/smb.conf; do true; done"; in
     ''
       cat > $TMPDIR/smb.conf <<SMB
       [global]
@@ -244,7 +246,7 @@ rec {
       SMB
 
       rm -f ./samba
-      ${socat}/bin/socat unix-listen:./samba exec:'/bin/sh -c ${sambaScript}',nofork > /dev/null 2>&1 &
+      ${socat}/bin/socat unix-listen:./samba exec:'${samba}/sbin/smbd -s $TMPDIR/smb.conf',nofork > /dev/null 2>&1 &
       while [ ! -e ./samba ]; do sleep 0.1; done # ugly
     '';
 
diff --git a/pkgs/os-specific/linux/kernel/cifs-timeout.patch b/pkgs/os-specific/linux/kernel/cifs-timeout.patch
new file mode 100644
index 00000000000..b2dac3f016c
--- /dev/null
+++ b/pkgs/os-specific/linux/kernel/cifs-timeout.patch
@@ -0,0 +1,47 @@
+diff -ru -x '*~' /tmp/linux-2.6.32.14/fs/cifs/transport.c linux-2.6.32.14/fs/cifs/transport.c
+--- /tmp/linux-2.6.32.14/fs/cifs/transport.c	2010-05-26 23:29:57.000000000 +0200
++++ linux-2.6.32.14/fs/cifs/transport.c	2010-06-20 22:03:13.000000000 +0200
+@@ -166,9 +166,9 @@
+ 			   after the retries we will kill the socket and
+ 			   reconnect which may clear the network problem.
+ 			*/
+-			if ((i >= 14) || (!server->noblocksnd && (i > 2))) {
++			if ((i >= 119) || (!server->noblocksnd && (i > 2))) {
+ 				cERROR(1,
+-				   ("sends on sock %p stuck for 15 seconds",
++				   ("sends on sock %p stuck for 120 seconds",
+ 				    ssocket));
+ 				rc = -EAGAIN;
+ 				break;
+@@ -459,11 +459,11 @@
+ 		goto out;
+ 
+ 	if (long_op == CIFS_STD_OP)
+-		timeout = 15 * HZ;
++		timeout = 120 * HZ;
+ 	else if (long_op == CIFS_VLONG_OP) /* e.g. slow writes past EOF */
+ 		timeout = 180 * HZ;
+ 	else if (long_op == CIFS_LONG_OP)
+-		timeout = 45 * HZ; /* should be greater than
++		timeout = 120 * HZ; /* should be greater than
+ 			servers oplock break timeout (about 43 seconds) */
+ 	else if (long_op == CIFS_ASYNC_OP)
+ 		goto out;
+@@ -651,7 +651,7 @@
+ 		goto out;
+ 
+ 	if (long_op == CIFS_STD_OP)
+-		timeout = 15 * HZ;
++		timeout = 120 * HZ;
+ 	/* wait for 15 seconds or until woken up due to response arriving or
+ 	   due to last connection to this server being unmounted */
+ 	else if (long_op == CIFS_ASYNC_OP)
+@@ -659,7 +659,7 @@
+ 	else if (long_op == CIFS_VLONG_OP) /* writes past EOF can be slow */
+ 		timeout = 180 * HZ;
+ 	else if (long_op == CIFS_LONG_OP)
+-		timeout = 45 * HZ; /* should be greater than
++		timeout = 120 * HZ; /* should be greater than
+ 			servers oplock break timeout (about 43 seconds) */
+ 	else if (long_op == CIFS_BLOCKING_OP)
+ 		timeout = 0x7FFFFFFF; /* large but no so large as to wrap */
diff --git a/pkgs/os-specific/linux/kernel/patches.nix b/pkgs/os-specific/linux/kernel/patches.nix
index 2e5232025dd..45e3174dc80 100644
--- a/pkgs/os-specific/linux/kernel/patches.nix
+++ b/pkgs/os-specific/linux/kernel/patches.nix
@@ -155,4 +155,11 @@ in
       features.aufsBase = true;
     };
 
+  # Increase the timeout on CIFS requests from 15 to 120 seconds to
+  # make CIFS more resilient to high load on the CIFS server.
+  cifs_timeout =
+    { name = "cifs-timeout";
+      patch = ./cifs-timeout.patch;
+    };
+  
 }