[DRBD-user] Help - synchronization

Diego Julian Remolina diego.remolina at ibb.gatech.edu
Thu Jun 15 13:58:56 CEST 2006

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


> An information is saved in an hard disk1(primary) but another 
> harddisk2(secondary) has not synchronized for any reason...

You mean Node1 and Node2. You use two machines for drbd, that implies two hard drives (each on 
separate computers), but the way you are stating it here, it seems like if you meant there were two 
hard drives in one machine which is not correct.

> In another moment the harddisk1(now secondary) is sychonized with the 
> another hard disk2(now primary). Right?
> But another information in the harddisk1 ?  Be will it lost ? This is 
> common with drbd ? How solve this ?

When you configured drbd (/etc/drbd.conf) you specified a protocol to be used on that resource. 
There are protocols A, B and C. If you are using protocol C (most secure for data integrity and 
recommended), then a write is not considered as commited, unless it was written to both primary and 
secondary nodes. So you should never loose any data if the two machines have healthy drbd 
connections. The only instances where you may loose data if you do not correct problems 
appropriately is when there is a split brain situation.

When Node2 becomes primary and Node1 becomes secondary, any writes made on Node2 will be correctly 
propragated to Node1 if the drbd connections are still fine. If your Node1 is drbd secondary and you 
need to reboot it, change hardware, reinstall the OS, etc, then when you boot it back up it will 
first synchronize the data from Node2 (if all the drbd configuration is still correct - would be 
need some work if you reinstalled the OS). This is all handled by drbd. You can reboot the machine 
and take a look at the logs and you will see messages like:

May 16 07:37:57 sauron kernel: drbd0: drbd0_receiver [3047]: cstate WFConnection --> WFReportParams
May 16 07:37:57 sauron kernel: drbd0: Handshake successful: DRBD Network Protocol version 74
May 16 07:37:57 sauron kernel: drbd0: Connection established.
May 16 07:37:57 sauron kernel: drbd0: I am(P): 1:00000002:00000002:00000055:0000000d:10
May 16 07:37:57 sauron kernel: drbd0: Peer(S): 1:00000002:00000002:00000054:0000000d:00
May 16 07:37:57 sauron kernel: drbd0: drbd0_receiver [3047]: cstate WFReportParams --> WFBitMapS
May 16 07:37:57 sauron kernel: drbd1: drbd1_receiver [3055]: cstate WFConnection --> WFReportParams
May 16 07:37:57 sauron kernel: drbd1: Handshake successful: DRBD Network Protocol version 74
May 16 07:37:57 sauron kernel: drbd1: Connection established.
May 16 07:37:57 sauron kernel: drbd1: I am(P): 1:00000002:00000002:00000041:0000000a:10
May 16 07:37:57 sauron kernel: drbd1: Peer(S): 1:00000002:00000002:00000041:00000009:00
May 16 07:37:57 sauron kernel: drbd1: drbd1_receiver [3055]: cstate WFReportParams --> WFBitMapS
May 16 07:37:58 sauron kernel: drbd1: Primary/Unknown --> Primary/Secondary
May 16 07:37:58 sauron kernel: drbd1: drbd1_receiver [3055]: cstate WFBitMapS --> SyncSource
May 16 07:37:58 sauron kernel: drbd1: Resync started as SyncSource (need to sync 1052680 KB [263170 
bits set]).
May 16 07:37:58 sauron kernel: drbd0: Primary/Unknown --> Primary/Secondary
May 16 07:37:58 sauron kernel: drbd0: drbd0_receiver [3047]: cstate WFBitMapS --> SyncSource
May 16 07:37:58 sauron kernel: drbd0: Resync started as SyncSource (need to sync 149756 KB [37439 
bits set]).
May 16 07:38:06 sauron kernel: drbd1: Primary/Secondary --> Secondary/Secondary
May 16 07:38:07 sauron kernel: drbd1: Secondary/Secondary --> Secondary/Primary
May 16 07:38:11 sauron kernel: drbd0: Resync done (total 13 sec; paused 0 sec; 11516 K/sec)
May 16 07:38:11 sauron kernel: drbd0: drbd0_worker [19823]: cstate SyncSource --> Connected
May 16 07:38:20 sauron kernel: drbd1: Resync done (total 22 sec; paused 0 sec; 47848 K/sec)
May 16 07:38:20 sauron kernel: drbd1: drbd1_worker [19824]: cstate SyncSource --> Connected

Hope this helps,

Diego


> 
> I wait for any help.
> Sorry, forget my hard english. I hope that understand me. :)
> Cya.
> 
> 
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