[DRBD-user] Data corruption risk in protocol A,C.

Wieck, Owen Owen.Wieck at ricardo.com
Fri Apr 24 17:18:27 CEST 2015

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


I think the short answer is no difference, and yes it will resync.  When your nodes become disconnected, there is a "replay of the changes" when they reconnect -- a resync operation.  This page describes it:


However, important note -- and this would be the same with both A and C protocols -- that resync is done from "front to back" of the block device, not in time/date order.  So for the duration of that resync operation, your secondary will be in an inconsistent state.  (Same goes for the write-ahead mode.  Use with caution!!)

As you noted, the main difference between A and C is if / when your primary node fails in some spectacular fashion (e.g. it blows up) you will lose acknowledged writes.  (Which is usually very bad.)

Warm Regards,

-----Original Message-----
From: drbd-user-bounces at lists.linbit.com [mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of Timofey Koolin
Sent: Friday, April 24, 2015 3:57 AM
To: drbd-user at lists.linbit.com
Subject: [DRBD-user] Data corruption risk in protocol A,C.

Is protocol A and C difference by data corruption risk?

I mean long time corruption when I have WAN replication with non ideal connections. Connection may be broken from time to time. Now I use protocol C. But I want to change it to protocol A.
I know about lost few last operations when I lost master node - it is OK.

I want to know - Has protocol A more data corruption risk then protocol C or not during replication. For example:
1. Write "123" to Master
2. Put data to tcp buffer in master, master return OK write data to OS.
3. Lost connection before data really send and accept by slave.

Will "123" put to slave after reconnect during resync process?
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