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DRBD é um amigo!
What is DRBD?
• DRBD is a block device designed as a building
block to form HA clusters.
• This is done by mirroring a who...
Block device (Kernel component)
File system
Buffer cache
Block device
Disk sched
Disk driver
DRBD sends I/O to the other node
File system
Buffer cache
DRBD
Disk sched
Disk driver
WRITE ops are sent
to secondary over...
Data flow in kernel land
How to set up DRBD
• Prepare DRBD partitions
• Create setup files
/etc/drbd.conf (DRBD-8.2)
/etc/drbd.d/global_common.conf...
DRBD settings
• In DRBD-8.2,
all the settings are in /etc/drbd.conf
• In DRBD-8.4,
global settings in /etc/drbd.d/global_c...
Sampe drbd.conf (1)
• global {
• usage-count no;
• }
• common {
• net {
• protocol C;
• }
• syncer {
• rate 100M;
• }
• }
Sample drbd.conf (2)
• resource r0 {
• protocol C;
• on Machine-HA1 { (must match what “uname –n” says on HA1)
• device /d...
Resource and Role
• In DRBD, every resource (partition) has a role,
which may be primary or secondary.
• A primary DRBD de...
Connection state
• DRBD always uses bond1
HA1: 10.0.128.17 (ping drbd1)
HA2: 10.0.128.18 (ping drbd2)
Monitor DRBD (1)
Healthy state
Shutdown bond1
Monitor DRBD (2)
Enabled bond1 again
DRBD became WFC status (Waiting For Connection)
Nothing can separate DRBD
Nada pode separar DRBD
What causes DRBD problems
There are 3 types of problems.
1. Network error (bond1)
 Outdated
2. Disk error (disk error or ...
1. Network problem
• When bond1 stops working between HA1 and
HA2, DRBD devices on standby node becomes
Outdated
How to fi...
Healthy State
Bond1 stopped (ifdown bond1)
CS (connection Status) becomes WFConnection (Waiting For Connection).
ST (Status) becomes Unk...
How to fix
• Find where the problem is. It can be bond1 on
HA1 or bond1 on HA2, or the network cable.
• Fix the network is...
Disk I/O error on secondary
• DRBD device will be Detached automatically
upon disk error.
• drbd.conf
Resource r0 {
disk {...
Disk I/O error on secondary
• Upon disk error, drbdadm detach <res> will run.
Secondary devices become Diskless state. Aft...
• Fix the disk issue at first.
• Then run drbdadm attach all
• Sync may run.
Disk I/O error on secondary
Disk I/O error on primary
• If disk I/O error happened on primary, Primary
DRBD devices become Diskless.
Disk I/O error on primary
• Fix the disk issue at first. Then run
drbdadm attach all on the bad node.
• Sync will run from...
• Attach/Detach
 attaches/detaches lower disks
• Connect/Disconnect
 connect-to/disconnect-from peer node
• Primary/Seco...
How to check if split-brain happens
• Once SB happens, you see
Split-Brain detected, dropping connection!
In /var/log/mess...
Sample plan to fix SB (1)
1. Take hostbackup
2. Identify the bad host
3. Identify which are primary and secondary
(DRBD)
4...
Sample plan to fix SB (2)
• drbdadm disconnect all (HA1 / HA2)
• drbdadm secondary all (HA1 / HA2)
• drbdadm disconnect al...
Sample plan to fix SB (3)
5. Start heartbeat on the good host to make it
Primary.
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DRBD é um amigo!

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Transcript of "DRBD é um amigo!"

  1. 1. DRBD é um amigo!
  2. 2. What is DRBD? • DRBD is a block device designed as a building block to form HA clusters. • This is done by mirroring a whole block device via an assigned network. • DRBD can be understand as network based RAID1. • T uses DRBD-8.2, S uses DRBD-8.4 (may change in the future).
  3. 3. Block device (Kernel component) File system Buffer cache Block device Disk sched Disk driver
  4. 4. DRBD sends I/O to the other node File system Buffer cache DRBD Disk sched Disk driver WRITE ops are sent to secondary over network
  5. 5. Data flow in kernel land
  6. 6. How to set up DRBD • Prepare DRBD partitions • Create setup files /etc/drbd.conf (DRBD-8.2) /etc/drbd.d/global_common.conf (DRBD-8.4) /etc/drbd.d/r0.res,r1.res (DRBD-8.4) • Start DRBD sync
  7. 7. DRBD settings • In DRBD-8.2, all the settings are in /etc/drbd.conf • In DRBD-8.4, global settings in /etc/drbd.d/global_common.conf resource level settings in /etc/drbd.d/r<N>.res • Sample: http://www.drbd.org/users-guide/re-drbdconf.html • HA1 and HA2 have the identical DRBD config files • Usage-count (always no) • Protocol (C  WRITE completes when reached the other node as well) • Sync rate (100MB/sec for sync  no need for 10Gb NIC) • Partition name (device minor # for /dev/drbdN) • Node name / IP address / port number
  8. 8. Sampe drbd.conf (1) • global { • usage-count no; • } • common { • net { • protocol C; • } • syncer { • rate 100M; • } • }
  9. 9. Sample drbd.conf (2) • resource r0 { • protocol C; • on Machine-HA1 { (must match what “uname –n” says on HA1) • device /dev/drbd1; • disk /dev/disk/by-label/XX; • address 10.0.128.17:7788; • } • on Machine-HA2 { (must match what “uname –n” says on HA2) • device /dev/drbd1; • disk /dev/disk/by-label/XX; • address 10.0.128.18:7788; • } • } • [root@Machine-HA2 ~]# uname -n • Machine-HA2 • [root@Machine-HA2 ~]#
  10. 10. Resource and Role • In DRBD, every resource (partition) has a role, which may be primary or secondary. • A primary DRBD device can be used for any read/write operations. • A DRBD secondary device can NOT be used for any read/write operations. • Secondary only receives WRITEs from primary.
  11. 11. Connection state • DRBD always uses bond1 HA1: 10.0.128.17 (ping drbd1) HA2: 10.0.128.18 (ping drbd2)
  12. 12. Monitor DRBD (1) Healthy state Shutdown bond1
  13. 13. Monitor DRBD (2) Enabled bond1 again DRBD became WFC status (Waiting For Connection)
  14. 14. Nothing can separate DRBD
  15. 15. Nada pode separar DRBD
  16. 16. What causes DRBD problems There are 3 types of problems. 1. Network error (bond1)  Outdated 2. Disk error (disk error or filesystem error)  Diskless 3. Role change without sync (typically caused by multiple host reboots)  Inconsistent
  17. 17. 1. Network problem • When bond1 stops working between HA1 and HA2, DRBD devices on standby node becomes Outdated How to fix?  • Fix the network issue at first. • Then DRBD will fix automatically. • Without heartbeat, you may need manual intervention.
  18. 18. Healthy State
  19. 19. Bond1 stopped (ifdown bond1) CS (connection Status) becomes WFConnection (Waiting For Connection). ST (Status) becomes Unknown on peer side. DS (Disk Status) becomes Outdated on secondary devices.
  20. 20. How to fix • Find where the problem is. It can be bond1 on HA1 or bond1 on HA2, or the network cable. • Fix the network issue. • Then the DRBD problem will be fixed automatically. • If heartbeat is NOT running, DRBD may not be fixed automatically.
  21. 21. Disk I/O error on secondary • DRBD device will be Detached automatically upon disk error. • drbd.conf Resource r0 { disk { on-io-error detach; } }
  22. 22. Disk I/O error on secondary • Upon disk error, drbdadm detach <res> will run. Secondary devices become Diskless state. After fixing the disk issue, You need to attach drbdadm attach all If the internal data on the disk is broken, sync will run from UpToDate device to the peer.
  23. 23. • Fix the disk issue at first. • Then run drbdadm attach all • Sync may run. Disk I/O error on secondary
  24. 24. Disk I/O error on primary • If disk I/O error happened on primary, Primary DRBD devices become Diskless.
  25. 25. Disk I/O error on primary • Fix the disk issue at first. Then run drbdadm attach all on the bad node. • Sync will run from UpToDate (secondary) to Inconsistent (Primary).
  26. 26. • Attach/Detach  attaches/detaches lower disks • Connect/Disconnect  connect-to/disconnect-from peer node • Primary/Secondary  define the role of resource • Invalidate  invalidate the data • Pre-DRBD-8.4 drbdadm -- --discard-my-data connect <res> DRBD-8.4 drbdadm connect --discard-my-data <res>  discard data on the resource
  27. 27. How to check if split-brain happens • Once SB happens, you see Split-Brain detected, dropping connection! In /var/log/messages • When SB happens, at least one node becomes StandAlone. The peer can be WFConnection or StandAlone too. • If SB happens, you need to discard data on one node.
  28. 28. Sample plan to fix SB (1) 1. Take hostbackup 2. Identify the bad host 3. Identify which are primary and secondary (DRBD) 4. Stop DB service heartbeat stop (HA1/HA2) make sure DRBD partitions are not mounted
  29. 29. Sample plan to fix SB (2) • drbdadm disconnect all (HA1 / HA2) • drbdadm secondary all (HA1 / HA2) • drbdadm disconnect all (HA1 / HA2) • drbdadm -- --discard-my-data connect all (only on bad host) • drbdadm connect all (good host) • drbdadm connect all (bad host)
  30. 30. Sample plan to fix SB (3) 5. Start heartbeat on the good host to make it Primary.
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