drivers/block/drbd/Kconfig v3.0-rc7

NOTE: In order to authenticate connections you have to select
CRYPTO_HMAC and a hash function as well.

DRBD is a shared-nothing, synchronously replicated block device. It
is designed to serve as a building block for high availability
clusters and in this context, is a "drop-in" replacement for shared
storage. Simplistically, you could see it as a network RAID 1.

Each minor device has a role, which can be 'primary' or 'secondary'.
On the node with the primary device the application is supposed to
run and to access the device (/dev/drbdX). Every write is sent to
the local 'lower level block device' and, across the network, to the
node with the device in 'secondary' state.  The secondary device
simply writes the data to its lower level block device.

DRBD can also be used in dual-Primary mode (device writable on both
nodes), which means it can exhibit shared disk semantics in a
shared-nothing cluster.  Needless to say, on top of dual-Primary
DRBD utilizing a cluster file system is necessary to maintain for
cache coherency.

For automatic failover you need a cluster manager (e.g. heartbeat).
See also: http://www.drbd.org/, http://www.linux-ha.org

If unsure, say N.

Say Y here if you want to simulate IO errors, in order to test DRBD's
behavior.

The actual simulation of IO errors is done by writing 3 values to
/sys/module/drbd/parameters/

enable_faults: bitmask of...
1     meta data write
2               read
4     resync data write
8                 read
16    data write
32    data read
64    read ahead
128   kmalloc of bitmap
256   allocation of EE (epoch_entries)

fault_devs: bitmask of minor numbers
fault_rate: frequency in percent

Example: Simulate data write errors on /dev/drbd0 with a probability of 5%.
echo 16 > /sys/module/drbd/parameters/enable_faults
echo 1 > /sys/module/drbd/parameters/fault_devs
echo 5 > /sys/module/drbd/parameters/fault_rate

If unsure, say N.