Caution
This is an advanced topic. Use at your own risk and ALWAYS backup your data before.
Useful Commands
View DRBD Status - DRBD 7
cat /proc/drbd
View DRBD Status - DRBD 9
drbdadm status
Reload all parameters
drbdadm adjust jtelshared
Disconnect the share (useful for planned maintenance)
drbdadm disconnect jtelshared
Down the share (useful for planned maintenance)
drbdadm down jtelshared
Up the share
drbdadm up jtelshared
Set the node to primary
drbdadm primary jtelshared
Connect the share
drbdadm connect jtelshared
PCS Cluster Commands (CentOS 8)
pcs cluster stop acd-store2 pcs cluster start acd-store2 pcs node standby acd-store2 pcs node unstandby acd-store2
Split Brain
Background
See also:
https://docs.linbit.com/doc/users-guide-84/s-resolve-split-brain/
Symptoms - CentOS 7 and earlier
cat /proc/drbd --> GIT-hash: a4d5de01fffd7e4cde48a080e2c686f9e8cebf4c build by mockbuild@, 2017-09-15 14:23:22 1: cs:StandAlone ro:Primary/Unknown ds:UpToDate/DUnknown r----- ns:0 nr:119823323 dw:119823323 dr:2128 al:0 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0
cs:StandAlone means the node is not connected.
This should be visible on both sides.
Symptoms - CentOS 8 and earlier
drbdadm status --> jtelshared role:Primary disk:UpToDate acd-store1 connection:Connecting drbdadm status --> # No currently configured DRBD found.
The first command shows that DRBD is active on the first node, but not active on the second node.
Note: this can be due to the second node being stopped or in standby.
Find out which node is active in the PCS cluster - CentOS 7
pcs status --> Cluster name: portal Stack: corosync Current DC: acd-store1 (version 1.1.16-12.el7_4.7-94ff4df) - partition with quorum Last updated: Sun Mar 18 18:05:32 2018 Last change: Fri Feb 16 00:07:51 2018 by root via cibadmin on acd-store2 2 nodes configured 3 resources configured Node acd-store1: standby Online: [ acd-store2 ] Full list of resources: Resource Group: haproxy_group ClusterDataJTELSharedMount (ocf::heartbeat:Filesystem): Started acd-store2 ClusterIP (ocf::heartbeat:IPaddr2): Started acd-store2 samba (systemd:smb): Started acd-store2 Daemon Status: corosync: active/enabled pacemaker: active/enabled pcsd: active/enabled
In the example above, the first node is in standby. The most important thing to check, is on which server the resources are started.
In this case, the resources are started on acd-store2.
This will therefore be defined as the NON BROKEN node.
Find out which node is active in the PCS cluster - CentOS 8
pcs status
-->
Cluster name: jtel_cluster
Cluster Summary:
* Stack: corosync
* Current DC: acd-lb1 (version 2.0.3-5.el8_2.1-4b1f869f0f) - partition with quorum
* Last updated: Sat Oct 3 12:39:22 2020
* Last change: Sat Oct 3 12:31:22 2020 by root via cibadmin on acd-lb2
* 2 nodes configured
* 5 resource instances configured
Node List:
* Online: [ acd-lb1 ]
* OFFLINE: [ acd-lb2 ]
Full List of Resources:
* Clone Set: DRBDClusterMount-clone [DRBDClusterMount] (promotable):
* Masters: [ acd-lb1 ]
* Stopped: [ acd-lb2 ]
* DRBDClusterFilesystem (ocf::heartbeat:Filesystem): Started acd-lb1
* Samba (systemd:smb): Started acd-lb1
* ClusterIP (ocf::heartbeat:IPaddr2): Started acd-lb1
Daemon Status:
corosync: active/enabled
pacemaker: active/enabled
pcsd: active/enabled
In the example above, the second node is offline. The most important thing to check, is on which server the resources are started.
In this case, the resources are started on acd-lb1.
This will therefore be defined as the NON BROKEN node.
Standby the broken node in the PCS cluster (if necessary)
This command can be run on either machine.
CentOS 7
pcs cluster standby acd-lb-broken --> Verify this with pcs status
CentOS 8
pcs node standby acd-lb-broken --> Verify this with pcs status
On broken node
Note: the first command will probably throw an error. Also, the share may not be mounted. This is OK.
umount /srv/jtel/shared drbdadm disconnect jtelshared drbdadm secondary jtelshared drbdadm connect --discard-my-data jtelshared
On the healthy node
drbdadm primary jtelshared drbdadm connect jtelshared
Check re-sync activity
The re-sync might take a long time.
Watch the status of this using:
cat /proc/drbd
Example output:
[root@storage01 ~]# cat /proc/drbd version: 8.4.10-1 (api:1/proto:86-101) GIT-hash: a4d5de01fffd7e4cde48a080e2c686f9e8cebf4c build by mockbuild@, 2017-09-15 14:23:22 1: cs:SyncTarget ro:Secondary/Primary ds:Inconsistent/UpToDate C r----- ns:0 nr:1411538 dw:121234862 dr:2128 al:0 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:184698664 [>....................] sync'ed: 0.8% (180368/181744)M finish: 26:12:15 speed: 1,940 (2,760) want: 2,120 K/sec
Tune the transfer (Second Node) - Only CentOS 7.x
Currently there is no procedure for tuning the transfer on CentOS 8.x
If the transfer is going to take ages, then tune it on the broken node:
drbdadm disk-options --c-plan-ahead=0 --resync-rate=110M jtelshared
Put broken node back to primary - CentOS 7.x ONLY
Do not do this on CentOS 8.x installations! Here DRBD is managed by the cluster.
drbdadm primary jtelshared --> Verify this with cat /proc/drbd
Restart PCS node
CentOS 7.x
pcs cluster unstandby acd-lb-broken --> Verify this with pcs status
CentOS 8.x
pcs cluster start acd-lb-broken pcs node unstandby acd-lb-broken --> Verify this with pcs status
Untune the transfer (Second Node) - CentOS 7x only
If the transfer was tuned, then untune it (on the broken node).
Note: it won't hurt to run this command anyway.
drbdadm adjust jtelshared
Check everything
pcs status # CentOS 7.x cat /proc/drbd # CentOS 8.x drbdadm status # On some other linux machines ls /home/jtel/shared # Windows dir //acd-store/shared
File System Corrupt
Sometimes, when DRBD fails, the file system will also become corrupt.
In this case both nodes might be primary, however neither will have the share mounted.
The command mount /srv/jtel/shared will fail.
In this case, it may be necessary to repair the file system.
Symptoms
[17354513.483526] XFS (drbd1): log mount/recovery failed: error -22 [17354513.483569] XFS (drbd1): log mount failed [17355040.104433] XFS (drbd1): Mounting V5 Filesystem [17355040.122234] XFS (drbd1): Corruption warning: Metadata has LSN (56:112832) ahead of current LSN (56:112733). Please unmount and run xfs_repair (>= v4.3) to resolve. [17355040.122239] XFS (drbd1): log mount/recovery failed: error -22 [17355040.122322] XFS (drbd1): log mount failed
Repairing
One one of the nodes (need to choose one to become primary):
xfs_repair /dev/drbd/by-res/jtelshared/0 pcs resource cleanup
This should then mount and start the resources on that node.
Then proceed with the other node as "broken" in the split brain situation.
Stalled Resync
If the DRBD resync stalls - the output will be "stalled" when cat /proc/drbd is executed - then it may be necessary to restart the machine.
This has been observed once, and restarting resolved the situation. However not much more is known about this state, or the cause, at this time.
Failed Connect (Unrelated data, aborting)
When the secondary has been told to discard it's data, and all of the commands to start the sync have been entered on both the healthy and the broken node, sometimes cat /proc/drbd will not report a connection.
Check /var/log/messages
If you can see output like this:
kernel: block drbd0: uuid_compare()=-1000 by rule 100 kernel: block drbd0: Unrelated data, aborting!
Then the metadata has become corrupt.
This requires that the metadata be completely reconstructed on the bad node.
Use the following commands to recreate the data on the broken node:
drbdadm down jtelshared drbdadm wipe-md jtelshared drbdadm create-md jtelshared
Then proceed with the re-sync as above (start with the part "On the broken node" with the commands to place this in secondary and discard data.
Failed Connect (Unknown Connection)
This produces errors something like this:
??: Failure: (162) Invalid configuration request additional info from kernel: unknown connection
In this case, drbd might not be loaded and enabled.
Execute the following code on the broken node and then proceed as above:
modprobe drbd systemctl enable drbd systemctl start drbd