Simulate a faulty block device with read errors?

Question

I\'m looking for an easier way to test my application against faulty block devices that generate i/o read errors when certain blocks are read. Trying to use a physical hard

Answer 1

It's not a loopback device you're looking for, but rather device-mapper.

Use dmsetup to create a device backed by the "error" target. It will show up in /dev/mapper/.

Page 7 of the Device mapper presentation (PDF) has exactly what you're looking for:

dmsetup create bad_disk << EOF
  0 8       linear /dev/sdb1 0
  8 1       error
  9 204791 linear /dev/sdb1 9
EOF

Or leave out the sdb1 parts to and put the "error" target as the device for blocks 0 - 8 (instead of sdb1) to make a pure error disk.

See also The Device Mapper appendix from "RHEL 5 Logical Volume Manager Administration".