[DRBD-user] writer order on secondary site

Digimer lists at alteeve.ca
Wed Dec 23 05:52:27 CET 2015

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

On 22/12/15 11:11 AM, Mia Lueng wrote:
> Hi:
> I'm just wondering how secondary handle the write ordering when a same
> block is written twice on primary.
> Application submits these updates: X, Y, Z.
> They may or may not be to the same block.
> If they are to the same block, then the application, file system
> or other layer already makes sure (or at least is supposed to do that),
> that the first update will finish before the second is submitted.
> These updates are replicated to the peer.
> When X,Y are to the same block, how secondary site make sure that the
> first update will finish before the second is summited?
> Thanks.

It will always be the same so long as the peer is connected. That is,
Primary writes X, change is sent to peer, write is confirmed complete.
Primary writes Y (repeat). The only thing that changes is is when the
primary considers the write to be complete which depends on your
protocol (c == hits storage on the peer, b == received on the peer's
network, a == hits the local machines network stack).

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