In case the specified DRBD device (minor number) does not exist yet, create it implicitly.

You can override DRBD's size determination method with this option. If you need to use the device before it was ever connected to its peer, use this option to pass the size of the DRBD device to the driver. Default unit is sectors (1s = 512 bytes).

If you use the size parameter in drbd.conf, we strongly recommend to add an explicit unit postfix. drbdadm and drbdsetup used to have mismatching default units.

If the driver of the lower_device reports an error to DRBD, DRBD will mark the disk as inconsistent, call a helper program, or detach the device from its backing storage and perform all further IO by requesting it from the peer. The valid err_handlers are: pass_on, call-local-io-error and detach.

Under fencing we understand preventive measures to avoid situations where both nodes are primary and disconnected (AKA split brain).

Valid fencing policies are:

dont-care

resource-only

resource-and-stonith

DRBD has four implementations to express write-after-write dependencies to its backing storage device. DRBD will use the first method that is supported by the backing storage device and that is not disabled. By default the flush method is used.

Since drbd-8.4.2 disk-barrier is disabled by default because since linux-2.6.36 (or 2.6.32 RHEL6) there is no reliable way to determine if queuing of IO-barriers works. Dangerous only enable if you are told so by one that knows for sure.

When selecting the method you should not only base your decision on the measurable performance. In case your backing storage device has a volatile write cache (plain disks, RAID of plain disks) you should use one of the first two. In case your backing storage device has battery-backed write cache you may go with option 3. Option 4 (disable everything, use "none") is dangerous on most IO stacks, may result in write-reordering, and if so, can theoretically be the reason for data corruption, or disturb the DRBD protocol, causing spurious disconnect/reconnect cycles. Do not use no-disk-drain.

Unfortunately device mapper (LVM) might not support barriers.

The letter after "wo:" in /proc/drbd indicates with method is currently in use for a device: b, f, d, n. The implementations:

barrier

flush

drain

none

Disables the use of disk flushes and barrier BIOs when accessing the meta data device. See the notes on --disk-flushes.

In some special circumstances the device mapper stack manages to pass BIOs to DRBD that violate the constraints that are set forth by DRBD's merge_bvec() function and which have more than one bvec. A known example is: phys-disk -> DRBD -> LVM -> Xen -> misaligned partition (63) -> DomU FS. Then you might see "bio would need to, but cannot, be split:" in the Dom0's kernel log.

The best workaround is to proper align the partition within the VM (E.g. start it at sector 1024). That costs 480 KiB of storage. Unfortunately the default of most Linux partitioning tools is to start the first partition at an odd number (63). Therefore most distributions install helpers for virtual linux machines will end up with misaligned partitions. The second best workaround is to limit DRBD's max bvecs per BIO (i.e., the max-bio-bvecs option) to 1, but that might cost performance.

The default value of max-bio-bvecs is 0, which means that there is no user imposed limitation.

To ensure smooth operation of the application on top of DRBD, it is possible to limit the bandwidth that may be used by background synchronization. The default is 250 KiB/sec, the default unit is KiB/sec.

Start resync on this device only if the device with minor is already in connected state. Otherwise this device waits in SyncPause state.

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. In case a primary node leaves the cluster unexpectedly, the areas covered by the active set must be resynced upon rejoining 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 1237. (Minimum: 7, Maximum: 65534)

See also drbd.conf(5) and drbdmeta(8) for additional limitations and necessary preparation.

DRBD's activity log transaction writing makes it possible, that after the crash of a primary node a partial (bit-map based) resync is sufficient to bring the node back to up-to-date. Setting al-updates to no might increase normal operation performance but causes DRBD to do a full resync when a crashed primary gets reconnected. The default value is yes.

The dynamic resync speed controller gets enabled with setting plan_time to a positive value. It aims to fill the buffers along the data path with either a constant amount of data fill_target, or aims to have a constant delay time of delay_target along the path. The controller has an upper bound of max_rate.

By plan_time the agility of the controller is configured. Higher values yield for slower/lower responses of the controller to deviation from the target value. It should be at least 5 times RTT. For regular data paths a fill_target in the area of 4k to 100k is appropriate. For a setup that contains drbd-proxy it is advisable to use delay_target instead. Only when fill_target is set to 0 the controller will use delay_target. 5 times RTT is a reasonable starting value. Max_rate should be set to the bandwidth available between the DRBD-hosts and the machines hosting DRBD-proxy, or to the available disk-bandwidth.

The default value of plan_time is 0, the default unit is 0.1 seconds. Fill_target has 0 and sectors as default unit. Delay_target has 1 (100ms) and 0.1 as default unit. Max_rate has 10240 (100MiB/s) and KiB/s as default unit.

We track the disk IO rate caused by the resync, so we can detect non-resync IO on the lower level device. If the lower level device seems to be busy, and the current resync rate is above min_rate, we throttle the resync.

The default value of min_rate is 4M, the default unit is k. If you want to not throttle at all, set it to zero, if you want to throttle always, set it to one.

If the lower-level device on which a DRBD device stores its data does not finish an I/O request within the defined disk-timeout, DRBD treats this as a failure. The lower-level device is detached, and the device's disk state advances to Diskless. If DRBD is connected to one or more peers, the failed request is passed on to one of them.

This option is dangerous and may lead to kernel panic!

"Aborting" requests, or force-detaching the disk, is intended for completely blocked/hung local backing devices which do no longer complete requests at all, not even do error completions. In this situation, usually a hard-reset and failover is the only way out.

By "aborting", basically faking a local error-completion, we allow for a more graceful swichover by cleanly migrating services. Still the affected node has to be rebooted "soon".

By completing these requests, we allow the upper layers to re-use the associated data pages.

If later the local backing device "recovers", and now DMAs some data from disk into the original request pages, in the best case it will just put random data into unused pages; but typically it will corrupt meanwhile completely unrelated data, causing all sorts of damage.

Which means delayed successful completion, especially for READ requests, is a reason to panic(). We assume that a delayed *error* completion is OK, though we still will complain noisily about it.

The default value of disk-timeout is 0, which stands for an infinite timeout. Timeouts are specified in units of 0.1 seconds. This option is available since DRBD 8.3.12.

Setting discard-zeroes-if-aligned to no will cause DRBD to always fall-back to zero-out on the receiving side, and to not even announce discard capabilities on the Primary, if the respective backend announces discard_zeroes_data=false.

Setting discards-zeroes-if-aligned to yes will allow DRBD to use discards, and to announce discard_zeroes=true, even on backends that announce discard_zeroes_data=false.

We used to ignore the discard_zeroes_data setting completely. To not break established and expected behaviour, the default value is yes.

This option is available since 8.4.7. See also drbd.conf(5).

Some disks announce WRITE_SAME support to the kernel but fail with an I/O error upon actually receiving such a request. This mostly happens when using virtualized disks -- notably, this behavior has been observed with VMware's virtual disks.

When disable-write-same is set to yes, WRITE_SAME detection is manually overriden and support is disabled.

The default value of disable-write-same is no. This option is available since 8.4.7.

The supported methods for load balancing of read requests are prefer-local, prefer-remote, round-robin, least-pending and when-congested-remote, 32K-striping, 64K-striping, 128K-striping, 256K-striping, 512K-striping and 1M-striping.

The default value of read-balancing is prefer-local. This option is available since 8.4.1.

When rs-discard-granularity is set to a non zero, positive value then DRBD tries to do a resync operation in requests of this size. In case such a block contains only zero bytes on the sync source node, the sync target node will issue a discard/trim/unmap command for the area.

The value is constrained by the discard granularity of the backing block device. In case rs-discard-granularity is not a multiplier of the discard granularity of the backing block device DRBD rounds it up. The feature only gets active if the backing block device reads back zeroes after a discard command.

The default value of rs-discard-granularity is 0. This option is available since 8.4.7.

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.

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 retries. The default value is 10. The unit is seconds.

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 value is 10. The unit is seconds.

If the partner node fails to send an expected response packet within val tenths of a second, the partner node is considered dead and therefore the TCP/IP connection is abandoned. The default value is 60 (= 6 seconds).

The socket send buffer is used to store packets sent to the secondary node, which are not yet acknowledged (from a network point of view) by the secondary node. When using protocol A, it might be necessary to increase the size of this data structure in order to increase asynchronicity between primary and secondary nodes. But keep in mind that more asynchronicity is synonymous with more data loss in the case of a primary node failure. Since 8.0.13 resp. 8.2.7 setting the size value to 0 means that the kernel should autotune this. The default size is 0, i.e. autotune.

Packets received from the network are stored in the socket receive buffer first. From there they are consumed by DRBD. Before 8.3.2 the receive buffer's size was always set to the size of the socket send buffer. Since 8.3.2 they can be tuned independently. A value of 0 means that the kernel should autotune this. The default size is 0, i.e. autotune.

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. To disable this feature, you should explicitly set it to 0; defaults may change between versions.

With this option the maximal number of write requests between two barriers is limited. Typically set to the same as --max-buffers, or the allowed maximum. Values smaller than 10 can lead to degraded performance. The default value is 2048.

With this option the maximal number of buffer pages allocated by DRBD's receiver thread is limited. Typically set to the same as --max-epoch-size. Small values could lead to degraded performance. The default value is 2048, the minimum 32. Increase this if you cannot saturate the IO backend of the receiving side during linear write or during resync while otherwise idle.

See also drbd.conf(5)

This setting has no effect with recent kernels that use explicit on-stack plugging (upstream Linux kernel 2.6.39, distributions may have backported).

When the number of pending write requests on the standby (secondary) node exceeds the unplug-watermark, we trigger the request processing of our backing storage device. Some storage controllers deliver better performance with small values, others deliver best performance when the value is set to the same value as max-buffers, yet others don't feel much effect at all. Minimum 16, default 128, maximum 131072.

With this option set you may assign primary role to both nodes. You only should use this option if you use a shared storage file system on top of DRBD. At the time of writing the only ones are: OCFS2 and GFS. If you use this option with any other file system, you are going to crash your nodes and to corrupt your data!

You need to specify the HMAC algorithm to enable peer authentication at all. You are strongly encouraged to use peer authentication. The HMAC algorithm will be used for the challenge response authentication of the peer. You may specify any digest algorithm that is named in /proc/crypto.

The shared secret used in peer authentication. May be up to 64 characters.

possible policies are:

disconnect

discard-younger-primary

discard-older-primary

discard-zero-changes

discard-least-changes

discard-node-NODENAME

possible policies are:

disconnect

consensus

discard-secondary

call-pri-lost-after-sb

violently-as0p

possible policies are:

disconnect

call-pri-lost-after-sb

violently-as0p

Normally the automatic after-split-brain policies are only used if current states of the UUIDs do not indicate the presence of a third node.

With this option you request that the automatic after-split-brain policies are used as long as the data sets of the nodes are somehow related. This might cause a full sync, if the UUIDs indicate the presence of a third node. (Or double faults have led to strange UUID sets.)

This option sets DRBD's behavior when DRBD deduces from its meta data that a resynchronization is needed, and the SyncTarget node is already primary. The possible settings are: disconnect, call-pri-lost and violently. While disconnect speaks for itself, with the call-pri-lost setting the pri-lost handler is called which is expected to either change the role of the node to secondary, or remove the node from the cluster. The default is disconnect.

With the violently setting you allow DRBD to force a primary node into SyncTarget state. This means that the data exposed by DRBD changes to the SyncSource's version of the data instantaneously. USE THIS OPTION ONLY IF YOU KNOW WHAT YOU ARE DOING.

DRBD can ensure the data integrity of the user's data on the network by comparing hash values. Normally this is ensured by the 16 bit checksums in the headers of TCP/IP packets. This option can be set to any of the kernel's data digest algorithms. In a typical kernel configuration you should have at least one of md5, sha1, and crc32c available. By default this is not enabled.

See also the notes on data integrity on the drbd.conf manpage.

DRBD usually uses the TCP socket option TCP_CORK to hint to the network stack when it can expect more data, and when it should flush out what it has in its send queue. There is at least one network stack that performs worse when one uses this hinting method. Therefore we introduced this option, which disable the setting and clearing of the TCP_CORK socket option by DRBD.

The time the peer has to answer to a keep-alive packet. In case the peer's reply is not received within this time period, it is considered dead. The default unit is tenths of a second, the default value is 5 (for half a second).

Use this option to manually recover from a split-brain situation. In case you do not have any automatic after-split-brain policies selected, the nodes refuse to connect. By passing this option you make this node a sync target immediately after successful connect.

Causes DRBD to abort the connection process after the resync handshake, i.e. no resync gets performed. You can find out which resync DRBD would perform by looking at the kernel's log file.

By default DRBD blocks when the available TCP send queue becomes full. That means it will slow down the application that generates the write requests that cause DRBD to send more data down that TCP connection.

When DRBD is deployed with DRBD-proxy it might be more desirable that DRBD goes into AHEAD/BEHIND mode shortly before the send queue becomes full. In AHEAD/BEHIND mode DRBD does no longer replicate data, but still keeps the connection open.

The advantage of the AHEAD/BEHIND mode is that the application is not slowed down, even if DRBD-proxy's buffer is not sufficient to buffer all write requests. The downside is that the peer node falls behind, and that a resync will be necessary to bring it back into sync. During that resync the peer node will have an inconsistent disk.

Available congestion_policys are block and pull-ahead. The default is block. Fill_threshold might be in the range of 0 to 10GiBytes. The default is 0 which disables the check. Active_extents_threshold has the same limits as al-extents.

The AHEAD/BEHIND mode and its settings are available since DRBD 8.3.10.

During online verification (as initiated by the verify sub-command), rather than doing a bit-wise comparison, DRBD applies a hash function to the contents of every block being verified, and compares that hash with the peer. This option defines the hash algorithm being used for that purpose. It can be set to any of the kernel's data digest algorithms. In a typical kernel configuration you should have at least one of md5, sha1, and crc32c available. By default this is not enabled; you must set this option explicitly in order to be able to use on-line device verification.

See also the notes on data integrity on the drbd.conf manpage.

A resync process sends all marked data blocks from the source to the destination node, as long as no csums-alg is given. When one is specified the resync process exchanges hash values of all marked blocks first, and sends only those data blocks over, that have different hash values.

This setting is useful for DRBD setups with low bandwidth links. During the restart of a crashed primary node, all blocks covered by the activity log are marked for resync. But a large part of those will actually be still in sync, therefore using csums-alg will lower the required bandwidth in exchange for CPU cycles.

During resync-handshake, the dirty-bitmaps of the nodes are exchanged and merged (using bit-or), so the nodes will have the same understanding of which blocks are dirty. On large devices, the fine grained dirty-bitmap can become large as well, and the bitmap exchange can take quite some time on low-bandwidth links.

Because the bitmap typically contains compact areas where all bits are unset (clean) or set (dirty), a simple run-length encoding scheme can considerably reduce the network traffic necessary for the bitmap exchange.

For backward compatibility reasons, and because on fast links this possibly does not improve transfer time but consumes cpu cycles, this defaults to off.

Introduced in 8.3.2.

In setups involving a DRBD-proxy and connections that experience a lot of buffer-bloat it might be necessary to set ping-timeout to an unusual high value. By default DRBD uses the same value to wait if a newly established TCP-connection is stable. Since the DRBD-proxy is usually located in the same data center such a long wait time may hinder DRBD's connect process.

In such setups socket-check-timeout should be set to at least to the round trip time between DRBD and DRBD-proxy. I.e. in most cases to 1.

The default unit is tenths of a second, the default value is 0 (which causes DRBD to use the value of ping-timeout instead). Introduced in 8.4.5.

Sets the cpu-affinity-mask for DRBD's kernel threads of this device. The default value of cpu-mask is 0, which means that DRBD's kernel threads should be spread over all CPUs of the machine. This value must be given in hexadecimal notation. If it is too big it will be truncated.

This setting controls what happens to IO requests on a degraded, disk less node (I.e. no data store is reachable). The available policies are io-error and suspend-io.

If ond-policy is set to suspend-io you can either resume IO by attaching/connecting the last lost data storage, or by the drbdadm resume-io res command. The latter will result in IO errors of course.

The default is io-error. This setting is available since DRBD 8.3.9.

Alias for --force.

Becoming primary fails if the local replica is not up-to-date. I.e. when it is inconsistent, outdated of consistent. By using this option you can force it into primary role anyway. USE THIS OPTION ONLY IF YOU KNOW WHAT YOU ARE DOING.

Since version 8.3.2, on-line verification should resume from the last position after connection loss. It may also be started from an arbitrary position by setting this option. If you had reached some stop-sector before, and you do not specify an explicit start-sector, verify should resume from the previous stop-sector.

Default unit is sectors. You may also specify a unit explicitly. The start-sector will be rounded down to a multiple of 8 sectors (4kB).

Since version 8.3.14, on-line verification can be stopped before it reaches end-of-device.

Default unit is sectors. You may also specify a unit explicitly. The stop-sector may be updated by issuing an additional drbdsetup verify command on the same node while the verify is running. This can be used to stop a running verify, or to update/shorten/extend the coverage of the currently running verify.

This command will fail if the device cannot communicate with its partner for timeout seconds. If the peer was working before this node was rebooted, the wfc_timeout is used. If the peer was already down before this node was rebooted, the degr_wfc_timeout is used. If the peer was successfully outdated before this node was rebooted the outdated_wfc_timeout is used. The default value for all those timeout values is 0 which means to wait forever. The unit is seconds. In case the connection status goes down to StandAlone because the peer appeared but the devices had a split brain situation, the default for the command is to terminate. You can change this behavior with the --wait-after-sb option.

A regular detach returns after the disk state finally reached diskless. As a consequence detaching from a frozen backing block device never terminates.

On the other hand A forced detach returns immediately. It allows you to detach DRBD from a frozen backing block device. Please note that the disk will be marked as failed until all pending IO requests where finished by the backing block device.

Show all configuration parameters, even the ones with default values. Normally, parameters with default values are not shown.

Include more information in the output even when it is likely redundant or irrelevant.

Include data transfer statistics in the output.

Colorize the output. With --color=auto, drbdsetup emits color codes only when standard output is connected to a terminal.

fs-backoffice role:Primary
  disk:UpToDate
  peer role:Secondary
    replication:Established peer-disk:UpToDate
	      

fs-data role:Primary suspended:no
    write-ordering:drain
  volume:0 minor:1 disk:UpToDate
      size:10616472 read:134465 written:144800 al-writes:18 bm-writes:0
      upper-pending:0 lower-pending:0 al-suspended:no blocked:no
  peer connection:Connected role:Secondary congested:no
    volume:0 replication:Established peer-disk:UpToDate resync-suspended:no
        received:122596 sent:22204 out-of-sync:0 pending:0 unacked:0
	      

Terminate after reporting the current state. The default is to continuously listen and report state changes.

Include statistics in the output.

Display the events of all DRBD minors.

This is a debugging aid that displays the content of all received netlink messages.

Clears the sync bitmap in addition to generating a new current UUID.

1.On both nodes, initialize meta data and configure the device.

drbdadm -- --force create-md res

2.They need to do the initial handshake, so they know their sizes.

drbdadm up res

3.They are now Connected Secondary/Secondary Inconsistent/Inconsistent. Generate a new current-uuid and clear the dirty bitmap.

drbdadm new-current-uuid --clear-bitmap res

4.They are now Connected Secondary/Secondary UpToDate/UpToDate. Make one side primary and create a file system.

drbdadm primary res

mkfs -t fs-type $(drbdadm sh-dev res)

1.drbdsetup new-current-uuid --clear-bitmap minor

2.Take the copy of the current active server. E.g. by pulling a disk out of the RAID1 controller, or by copying with dd. You need to copy the actual data, and the meta data.

3.drbdsetup new-current-uuid minor