Appendix A. Recent changes

Table of Contents

A.1. Volumes
A.1.1. Changes to udev symlinks
A.2. Changes to the configuration syntax
A.2.1. Boolean configuration options
A.2.2. syncer section no longer exists
A.2.3. protocol option is no longer special
A.2.4. New per-resource options section
A.3. On-line changes to network communications
A.3.1. Changing the replication protocol
A.3.2. Changing from single-Primary to dual-Primary replication
A.4. Changes to the drbdadm command
A.4.1. Changes to pass-through options
A.4.2. --force option replaces --overwrite-data-of-peer
A.5. Changed default values
A.5.1. Number of concurrently active Activity Log extents (al-extents)
A.5.2. Run-length encoding (use-rle)
A.5.3. I/O error handling strategy (on-io-error)
A.5.4. Variable-rate synchronization
A.5.5. Number of configurable DRBD devices (minor-count)

This appendix is for users who upgrade from earlier DRBD versions to DRBD 8.4. It highlights some important changes to DRBD’s configuration and behavior.

A.1. Volumes

Volumes are a new concept in DRBD 8.4. Prior to 8.4, every resource had only one block device associated with it, thus there was a one-to-one relationship between DRBD devices and resources. Since 8.4, multiple volumes (each corresponding to one block device) may share a single replication connection, which in turn corresponds to a single resource.

A.1.1. Changes to udev symlinks

The DRBD udev integration scripts manage symlinks pointing to individual block device nodes. These exist in the /dev/drbd/by-res and /dev/drbd/by-disk directories.

In DRBD 8.3 and earlier, links in /dev/drbd/by-disk point to single block devices:

udev managed DRBD symlinks in DRBD 8.3 and earlier. 

lrwxrwxrwx 1 root root 11 2011-05-19 11:46 /dev/drbd/by-res/home ->
  ../../drbd0
lrwxrwxrwx 1 root root 11 2011-05-19 11:46 /dev/drbd/by-res/data ->
  ../../drbd1
lrwxrwxrwx 1 root root 11 2011-05-19 11:46 /dev/drbd/by-res/nfs-root ->
  ../../drbd2

In DRBD 8.4, since a single resource may correspond to multiple volumes, /dev/drbd/by-res/<resource> becomes a directory, containing symlinks pointing to individual volumes:

udev managed DRBD symlinks in DRBD 8.4. 

lrwxrwxrwx 1 root root 11 2011-07-04 09:22 /dev/drbd/by-res/home/0 ->
  ../../drbd0
lrwxrwxrwx 1 root root 11 2011-07-04 09:22 /dev/drbd/by-res/data/0 ->
  ../../drbd1
lrwxrwxrwx 1 root root 11 2011-07-04 09:22 /dev/drbd/by-res/nfs-root/0 ->
  ../../drbd2
lrwxrwxrwx 1 root root 11 2011-07-04 09:22 /dev/drbd/by-res/nfs-root/1 ->
   ../../drbd3

Configurations where filesystems are referred to by symlink must be updated when moving to DRBD 8.4, usually by simply appending /0 to the symlink path.