blkmapd - Linux

Overview

blkmapd is a utility that provides a device mapper target to manage physical disks and logical volumes. It is typically used in conjunction with dmsetup to create and manage device mapper devices.

Syntax

blkmapd [OPTIONS...] DEVICES

Options/Flags

  • -b | --blocksize : Set the block size for the device (default: 512)
  • -c | --cache : Set the size of the in-memory cache (default: 16MB)
  • -d | --debug: Enable debugging output
  • -f | --flush: Flush all mapped blocks to disk before exit
  • -h | --help: Display help information
  • -l | --log : Set the log file (default: syslog)
  • -m | --map : Set the mapping file (default: /etc/blkmapd.conf)
  • -n | --no-flush: Disable flushing of mapped blocks to disk
  • -p | --pid : Set the PID file (default: /var/run/blkmapd.pid)
  • -s | --status: Print the status of the device mapper devices
  • -v | --version: Display version information

Examples

Create a striped device

dmsetup create striped /dev/sd{a,b} --table "0 256 linear /dev/sdc 0"

Create a mirrored device

dmsetup create mirror /dev/sd{a,b} --table "0 256 linear /dev/sdc 0 256 linear /dev/sdd 0"

Create a RAID-5 device

dmsetup create raid5 /dev/sd{a,b,c,d,e} --table "0 256 raid5 /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/sdg 0"

Print the status of the device mapper devices

blkmapd -s

Common Issues

The device mapper device is not recognized by the system

This can happen if the device mapper module is not loaded. To load the module, run the following command:

modprobe dm_mod

The device mapper device is not responding

This can happen if the blkmapd process has crashed. To restart the process, run the following command:

systemctl restart blkmapd

Integration

blkmapd can be combined with other Linux commands or tools to perform more advanced tasks. For example, the following command can be used to create a RAID-1 device and mount it:

dmsetup create mirror /dev/md1 --table "0 256 linear /dev/sdc 0 256 linear /dev/sdd 0"
mkfs.ext4 /dev/md1
mount /dev/md1 /mnt/raid1

Related Commands

  • dmsetup – Device mapper command
  • mdadm – RAID management command