[DRBD-user] Question about 3 nodes, three way replication with WAN link
pfaf at wisdomsoftware.net
Thu Feb 3 23:21:41 CET 2022
I would like to ask, is if we can have three DRBD nodes like below:
Main Site DR Site
Server A (primary) Server B (primary) Server C (offsite
Layer 1 Physical Disks Physical Disks Physical Disks
| | |
Layer 2 LVM LVM LVM
| | |
Layer 3 DRBD <--*Protocol C*---> DRBD DRBD
(with no DRBD partner)
| | |
Layer 4 *Stacked DRBD* *Stacked DRBD* <-*WAN/Protocol A*-> *Stacked DRBD*
| | |
Layer 5 LVM Inactive LVM Inactive LVM
| | |
Layer 6 Filesystem Unmounted Filesystem Unmounted Filesystem
| | |
Layer 7 Applications+VMs NotUsed/Standby NotUsed/Standby
This use-case is like the diagram shown and discussed in the link below
but the data are replicated to the third server using the secondary
server (ServerB) as a primary read-only server.
This way, even if the writing application will block, it will only
affect ServerB while ServerA will continue running at full speed,
this is what we actually hope for at least.
a) Layer 3 *DRBD *is *Primary *on *all servers*.
b) Layer 4 *Stacked DRBD* is *Primary *on both *ServerA *and *ServerB*
(allow-two-primaries). *Stacked DRBD* on *ServerC***is *Secondary* and
replicates from *ServerB*.
c) ServerB will be used for off-site replication to ServerC, so that the
slow speed of the WAN link used for replication does not affect ServerA.
Since ServerB and ServerC will be used as backup servers,
actually as hot stand-by in read-only mode(LVM will be in
_is there any possibility that we may have any data corruption?_
/I believe that there should not be any data corruption since ServerB
will only act as read-only server and will be used only for the off-site
We understand that in the above scenario Stacked DRBD metadata and disk
data are only written from ServerA
since ServerA is the only server that has Layer5, Layer6 and Layer7
If ServerB should ever become Primary for the LVM partition in Layer5,
we would first unmount LVM partition in Layer5, ,
the WAN replication would be switched from between ServerB and ServerC
to between ServerA and ServerC,
and afterwards ServerB would mount Layer5 LVM, Layer6 Filesystem and
Then ServerB would be the only server to write data, and ServerA would
send data to ServerC...
Do you think we are bound to have any corruption in the above scenario,
if we make sure that Layer5 LVM and the above Layers will never be
mounted on more that one servers at a time?
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