resource drbd0 {
  protocol C;
  incon-degr-cmd "halt -f";

on thost1 { device /dev/drbd1; disk /dev/hda7; address 10.1.1.31:7789; meta-disk internal; }

on thost2 { device /dev/drbd1; disk /dev/hda7; address 10.1.1.32:7789; meta-disk internal; } } In this example there is a single DRBD resource (called drbd0) which uses protocol C for the connection between its devices. The device which runs on host thost1 uses /dev/drbd1 as devices for its application, and /dev/hda7 as low level storage for the data. The IP addresses are used to specify the networking interfaces to use.

There may be multiple resource sections in a single drbd.conf file. For more examples please have a look at the DRBD Quickstart Guide <URL:http://www.linux-ha.org/DRBD/QuickStart07>.

skip

Comments out chunks of text, even spanning more than one line. Characters between the keyword skip and the opening brace (``{'')are ignored. Everything enclosed by the braces is skipped. This comes in handy, if you just want to comment out some 'resource [name] {...}' section: just precede it with 'skip'.

global

Configures some global parameters. Currently only minor-count, dialog-refresh and disable-ip-verification are allowed here. You may only have one global section, preferably as the first section.

resource name

Configures a DRBD resource. Each resource section needs to have two on host sections and may have a startup, a syncer, a net and a disk section. Required parameter in this section: protocol. Optional parameter: incon-degr-cmd.

on host-name

Carries the necessary configuration parameters for a DRBD device of the enclosing resource. host-name is mandatory and must match the linux hostname (uname -n) of one of the nodes. Required parameters in this section: device, disk, address, meta-disk.

disk

This section is used to fine tune DRBD's properties in respect to the low level storage. Please refer to drbdsetup(8) for detailed description of the parameters. Optional parameter: on-io-error, size.

net

This section is used to fine tune DRBD's properties. Please refer to drbdsetup(8) for detailed description of this section's parameters. Optional parameters: sndbuf-size, timeout, connect-int, ping-int, max-buffers, max-epoch-size, ko-count, on-disconnect.

startup

This section is used to fine tune DRBD's properties. Please refer to drbdsetup(8) for detailed description of this section's parameters. Optional parameters: wfc-timeout, degr-wfc-timeout.

syncer

This section is used to fine tune the synchronisation daemon for the device. Please refer to drbdsetup(8) for detailed description of this section's parameters. Optional parameters: rate, group, al-extents.

minor-count count

count may be a number from 1 to 255.

Use minor-count if you want to define more resources later without reloading the DRBD kernel module. Per default the module loads with exactly as many devices as configured in this file. Built-in default for module is 2, and 8 for monolithic kernel. For monolithic kernel minor-count is ignored, and you have to pass a kernel boot parameter drbd.minor_count=count to change the default.

dialog-refresh time

time may be 0 or a positive number.

The user dialog redraws the second count every time seconds (or does no redraws if time is zero). The default is 1.

disable-ip-verification

Use disable-ip-verification if, for some obscure reasons, drbdadm can/might not use ip or ifconfig to do a sanity check for the IP address, you can disable it with this this option.

protocol prot-id

On the TCP/IP link the specified protocol is used. Valid protocol specifiers are A, B, and C.

Protocol A: write IO is reported as completed, if it has reached local disk and local TCP send buffer.

Protocol B: write IO is reported as completed, if it has reached local disk and remote buffer cache.

Protocol C: write IO is reported as completed, if it has reached both local and remote disk.

incon-degr-cmd command

In case a node starts up in degraded mode (degr-wfc-timeout is set) and its local replica of the data is inconsistent it executes the command. If the command exits without error, drbddisk expects the DRBD device to be in primary state.

device name

The name of the block device node of the resource being described. You must use this device with your application (file system) and you must not use the low level block device which is specified with the disk parameter.

The device nodes must have the same major number as the DRBD driver has. With the current implementation major 147 is used and the corresponding device nodes are usually named /dev/drbd0, /dev/drbd1, etc. ( All releases before drbd-0.7.1 used major 43 and the device files /dev/nb*. )

Installation scripts of the DRBD package provide, that /dev/drbd0 to /dev/drbd8 are predefined in your system. To be sure, issue something like ls /dev/drbd*.

disk name

DRBD uses this block device to actually store and retrieve the data. Never access such a device while DRBD is running on top of it. This holds also true for dumpe2fs(8) and similar commands.

address IP:port

A resource needs one IP address per device, which is used to wait for incoming connections from the partner device respectively to reach the partner device.

Each DRBD resource needs a TCP port which is used to connect to the node's partner device. Two different DRBD resources may not use the same IP:port combination on the same node.

meta-disk internal

meta-disk device [index]

internal means, that the last 128 MB of the lower device are used to store the meta-data. You must not use [index] with internal.

You can use a single block device to store meta-data of multiple DRBD devices. E.g. use meta-disk /dev/hde6[0]; and meta-disk /dev/hde6[1]; for two different resources. In this case the meta-disk would need to be at least 256 MB in size.

on-io-error handler

handler is taken, if the lower level device reports io-error to the upper layers.

handler may be pass_on, panic, or detach.

pass_on: Report the io-error to the upper layers. On Primary report it to the mounted file system. On Secondary ignore it.

panic: The node leaves the cluster by doing a kernel panic.

detach: The node drops its low level device, and continues in disk less mode.

sndbuf-size size

size is size of the TCP socket send buffer. Default is 128K. You can specify smaller or larger values. Larger values are appropriate for reasonable write throughput with protocol A over high latency networks. Very large values like 1M may cause problems. Even values below 32K do not make much sense.

timeout time

If the partner node fails to send an expected response packet within time 10ths of a second, the partner node is considered dead and therefore the TCP/IP connection is abandoned. This must be lower than connect-int and ping-int. The default value is 60 = 6 seconds, the unit 0.1 seconds.

connect-int time

In case it is not possible to connect to the remote DRBD device immediately, DRBD keeps on trying to connect. With this option you can set the time between two tries. The default value is 10 seconds, the unit is 1 second.

ping-int time

If the TCP/IP connection linking a DRBD device pair is idle for more than time seconds, DRBD will generate a keep-alive packet to check if its partner is still alive. The default is 10 seconds, the unit is 1 second.

max-buffers number

Maximal number of requests to be allocated by DRBD. Unit is PAGE_SIZE, which is 4 KB on most systems. The minimum is hardcoded to 32 (=128 KB). For high performance installations it might help, if you increase that number. These buffers are used to hold datablocks while they are written to disk.

max-epoch-size number

The highest number of data blocks between two write barriers. If you set this smaller than 10 you might decrease your performance.

ko-count count

In case the secondary node fails to complete a single write request for count times the timeout, it is expelled from the cluster. (I.e. the primary node goes into StandAlone mode.) The default is 0, which disables this feature.

on-disconnect handler

When the connection to the peer is lost, DRBD can either go into stand alone mode, try to reconnect to the peer or freeze all further IO requests (think of an NFS hard mount). Valid handler specifiers are stand_alone, reconnect and freeze_io. The default handler is reconnect.

stand_alone: Do not reconnect, go into StandAlone state.

reconnect: Try to reconnect.

freeze_io: Try to reconnect, but freeze all IO until the connection is established again.

wfc-timeout time

Wait for connection timeout. The init script drbd(8) blocks the boot process until the DRBD resources are connected. This is so when the cluster manager starts later, it does not see a resource with internal split-brain. In case you want to limit the wait time, do it here. Default is 0, which means unlimited. Unit is seconds.

degr-wfc-timeout time

Wait for connection timeout, if this node was a degraded cluster. In case a degraded cluster (= cluster with only one node left) is rebooted, this timeout value is used instead of wfc-timeout, because the peer is less likely to show up in time, if it had been dead before. Default is 60, unit is seconds. Value 0 means unlimited.

rate rate

To ensure smooth operation of the application on top of DRBD, it is possible to limit the bandwidth which may be used by background synchronizations. The default is 250 KB/sec, the default unit is KB/sec. Optional suffixes K, M, G are allowed.

group number

Resynchronization of all devices in one group runs parallel. Groups are serialized in ascending order. You should avoid, that devices which lower devices share one and the same physical disk sync in parallel. The default group is 0. I.e. per default all devices sync parallel. Negative and positive numbers are allowed.

al-extents extents

DRBD automatically performs hot area detection. With this parameter you control how big the hot area (=active set) can get. Each extent marks 4M of the backing storage (=low level device). In case a primary node leaves the cluster unexpectedly the areas covered by the active set must be resynced upon rejoin of the failed node. The data structure is stored in the meta-data area, therefore each change of the active set is a write operation to the meta-data device. A higher number of extents gives longer resync times but less updates to the meta-data. The default number of extents is 127. (Minimum: 7, Maximum: 3843)