diff --git a/iscsi-scst/README b/iscsi-scst/README
index 71501c323..b2227d25a 100644
--- a/iscsi-scst/README
+++ b/iscsi-scst/README
@@ -952,6 +952,39 @@ disable_sendpage parameter for drbd module. But in this case it might be
 better for performance simply not apply put_page_callback patch.
 
 
+Background information about zero-copy data sending
+---------------------------------------------------
+
+As explained above the most efficient operation of the iSCSI-SCST target
+driver is achieved when the following two conditions are met:
+* Data is sent from target to initiator in a zero-copy fashion.
+* Data buffers are cached for reuse (by the so-called sgv pool). 
+Unfortunately the zero-copy API in the Linux kernel (proto.sendpage() /
+tcp_sendpage()) does not yet support completion notifications. Hence the
+put_page_callback patch which adds completion notification support to
+tcp_sendpage(). However, since the put_page_callback patch increases the size
+of the page structure in the Linux kernel that patch is considered
+unacceptable for integration in the mainline kernel [1]. Another approach,
+called skb paged fragment destructors, might get merged in the mainline kernel
+in the future. Version five of that patch series has been posted in May 2012
+[2].
+
+Notes:
+* The current implementation of scst_user is such that iSCSI-SCST only sends
+  data allocated by scst_user in a zero-copy fashion if the put_page_callback
+  patch has been applied. This holds even if scst_user did not use the sgv
+  pool to allocate a data buffer.
+* Zero-copy sending is only possible with network interface drivers that
+  support scatter/gather and checksumming (NETIF_F_SG and NETIF_F_ALL_CSUM
+  respectively). 
+
+References:
+[1] James Bottomley, Linux Kernel Mailing List, December 2008,
+    http://lkml.org/lkml/2008/12/11/213.
+[2] Ian Campbell, [PATCH v5 0/9] skb paged fragment destructors, May 3 2012,
+    linux-netdev, http://marc.info/?l=linux-netdev&m=133605705111948&w=2.
+
+
 Credits
 -------
 
diff --git a/scst/README.drbd b/scst/README.drbd
new file mode 100644
index 000000000..dbb6cc6a5
--- /dev/null
+++ b/scst/README.drbd
@@ -0,0 +1,46 @@
+SCST, DRBD and Dual Primary Mode
+********************************
+
+Introduction
+------------
+One possible approach to build a highly available storage solution is to
+combine SCST with DRBD. While designing such a solution one has to choose an
+operation mode for DRBD. While single primary mode is the easiest to set up,
+with dual primary mode it becomes possible to balance the load for a single
+LUN over the clustered servers. However, SCST and DRBD settings have to be
+chosen carefully in order to avoid data corruption with dual primary
+mode. One must make sure that SCST only confirms a write as finished to the
+multipath initiator after the data involved in write operation has been
+passed on to DRBD on both nodes.
+
+SCST Configuration
+------------------
+In order to avoid data corruption it is crucial to use the following SCST
+settings for each DRBD block device exported via SCST:
+* One can use either the vdisk_blockio device handler or vdisk_fileio.
+* Caching MUST be disabled: set the nv_cache parameter to 0 in scst.conf.
+* Write-through MUST be enabled: set the write_through parameter to 1 in
+  scst.conf.
+
+DRBD Configuration
+------------------
+As documented in the DRBD manual, dual primary mode only works with the DRBD
+replication protocol C and not with protocol A nor with protocol B.
+
+Initiator Configuration
+-----------------------
+When using VMware, do NOT use multipath I/O in round-robin mode. This mode
+namely depends on persistent reservations to guarantee data
+consistency. When running an SCST cluster, the SCST persistent reservation
+state is not shared between the two nodes.
+
+References
+----------
+* DRBD authors, [Dual Primary Mode], DRBD Manual, 2011.
+* VMware, [iSCSI SAN Configuration Guide 4.1], VMware website, September 2010.
+* Phil White, [VMware ESX, MPIO, SCST and DRBD in Dual Primary Mode], SCST
+  Developers Mailing List, June 2010.
+* Stefan Berger, [SCST and DRBD in Dual Primary Mode], DRBD users mailing
+  list, June 2010.
+* Bart Van Assche [SCST and DRBD in Dual Primary Mode], SCST Developers
+  Mailing List, May 2011.