Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 20/04/16 02:15 PM, akan tortz wrote: > Hi ALL, > > I’m new to DRBD. > The goal is to have an asynchronous replication once or twice a day > between the nodes. > > Is this possible with DRBD without DRBD proxy solution? > > From what I’ve tested I see that the secondary node can be in a > disconnected state (drbdadm disconnect <resource>) but I don’t know how > long. > Another concern is how much changes (writes) can accommodate the primary > node while the secondary is offline? Protocol A states that the local > writes are completed once the local disk write is finished and the > replication packet is placed in the local TCP send buffer. So that means > if TCP send buffer is full then DRBD will block all write operations? > > Thanks. The peer can be disconnected as long as you want. As inodes change, they're marked dirty (oos:X in /proc/drbd). When the peer connects, it starts copying those dirty blocks over at the resync rate (dynamic on 8.4, generally <30% of available performance *at most*). At worst, all inodes eventually change and the full device needs to be resynced. The protocols determine how changes are handled in a connected state (replication, as opposed to resync). Replication always goes as fast as possible (maximum write speed less what is being consumed during a resync operation). The protocol determines when DRBD will report the write complete to the upper level application. In protocol A, that happens as soon as the data is on the outbound network buffer. Protocol C waits until the peer confirms the data made it to persistent storage. Thus, Protocol A is async replication where protocol C is sync replication. When the peer is disconnected, no replication is attempted so the protocol has no meaning. The inode(s) are marked dirty and it's done. -- Digimer Papers and Projects: https://alteeve.ca/w/ What if the cure for cancer is trapped in the mind of a person without access to education?