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 peer_requests
512 insert data corruption on receiving side

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.