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Dear all,<br>
<br>
I would like to ask, is if we can have three DRBD nodes like below:<br>
<br>
<font size="4" face="monospace"> Main
Site DR Site<br>
Server A (primary) Server B (primary)
Server C (offsite secondary)<br>
=============================== ================================
============================<br>
Layer 1 Physical Disks </font><font size="4"
face="monospace"><font size="4" face="monospace">Physical
Disks </font></font><font size="4"
face="monospace">Physical Disks<br>
| |
|<br>
Layer 2 LVM </font><font size="4"
face="monospace"><font size="4" face="monospace">LVM
</font></font><font size="4" face="monospace"><font size="4"
face="monospace"><font size="4" face="monospace">LVM<br>
</font></font></font><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"> |
| |<br>
</font>Layer 3 DRBD <--<b>Protocol C</b>--->
DRBD DRBD (with no DRBD partner)<br>
</font></font></font><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"> |
| |<br>
</font>Layer 4 <b><font color="green">Stacked DRBD</font></b>
<font color="green"><b>Stacked DRBD</b></font> <-<b>WAN/Protocol
A</b>-> <font color="blue"><b>Stacked DRBD</b></font><br>
</font></font></font><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4"
face="monospace"> |
| |<br>
</font></font></font></font>Layer 5
LVM Inactive LVM </font></font></font><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace">Inactive
LVM<br>
</font></font></font></font></font></font><font size="4"
face="monospace"><font size="4" face="monospace"><font size="4"
face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace">
|
| |<br>
</font></font></font></font>Layer 6 Filesystem
Unmounted Filesystem </font></font></font><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace">Unmounted
Filesystem</font></font></font> </font></font></font><br>
<font size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4"
face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace">
|
| |<br>
Layer 7 Applications+VMs
NotUsed/Standby </font></font></font></font></font></font></font></font></font></font><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4"
face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4"
face="monospace"><font size="4"
face="monospace"><font size="4"
face="monospace"><font size="4"
face="monospace"><font size="4"
face="monospace"><font size="4"
face="monospace"><font size="4"
face="monospace"><font size="4"
face="monospace"><font size="4"
face="monospace"><font
size="4" face="monospace">NotUsed/Standby</font></font></font></font></font></font></font></font></font></font>
</font></font></font></font></font></font></font><br>
<br>
</font></font></font><font size="4"><font size="4"><font
size="4"><br>
This use-case is like the diagram shown and discussed in the
link below<br>
</font></font></font><font size="4"><font size="4"><font
size="4"><font size="4"><font size="4"><font size="4"><a
moz-do-not-send="true"
href="https://linbit.com/drbd-user-guide/users-guide-drbd-8-4/#s-three-way-repl"
class="moz-txt-link-freetext">https://linbit.com/drbd-user-guide/users-guide-drbd-8-4/#s-three-way-repl</a></font></font></font><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"></font></font></font><br>
but the data are replicated to the third server using the
secondary server (ServerB) as a primary read-only server.<br>
This way, even if </font></font></font><font size="4"><font
size="4"><font size="4">the writing application will block, it
will only affect ServerB while ServerA will continue running
at full speed,<br>
this is what we actually hope for at least.<br>
</font></font></font><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><br>
</font></font></font><font size="4"><font size="4"><font
size="4">Notes:<br>
a) Layer 3 <b>DRBD </b>is <b>Primary </b>on <b>all
servers</b>.<br>
b) Layer 4 <font color="green"><b>Stacked DRBD</b></font> is
<font color="green"><b>Primary </b></font>on both <b><font
color="green">ServerA </font></b>and <b><font
color="green">ServerB</font></b> (</font></font></font><font
size="4"><font size="4"><font size="4"><span class="ILfuVd"><span
class="hgKElc">allow-two-primaries</span></span>). <b><font
color="blue">Stacked DRBD</font></b> on <b><font
color="blue">ServerC</font></b><b> </b>is <font
color="blue"><b>Secondary</b></font> and replicates from </font></font></font><font
size="4"><font size="4"><font size="4"><font size="4"><font
size="4"><font size="4"><b><font color="green">ServerB</font></b>.</font></font></font>
<br>
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.<br>
<br>
Since ServerB and ServerC will be used as backup servers, <br>
actually as hot stan</font></font></font><font size="4"><font
size="4"><font size="4">d-by in read-only mode</font></font></font><font
size="4"><font size="4"><font size="4"> (LVM will be in
"not-available/unavailable" mode),</font></font></font><font
size="4" face="monospace"><font size="4" face="monospace"><font
size="4" face="monospace"><br>
</font></font></font><font size="4"><font size="4"><font
size="4"><u>is there any possibility that we may have any data
corruption?</u><br>
<br>
<i>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 replication.</i><i><br>
</i><br>
We understand that in the above scenario Stacked DRBD metadata
and disk data are only written from ServerA <br>
since </font></font></font><font size="4"><font size="4"><font
size="4"><font size="4"><font size="4"><font size="4">ServerA
is </font></font></font>the only server
that has Layer5, Layer6 and Layer7 mounted, correct?<br>
<br>
If ServerB should ever become Primary for the LVM partition in
Layer5,<br>
we would first unmount LVM partition in Layer5, , <br>
the </font></font></font><font size="4"><font size="4"><font
size="4"><font size="4"><font size="4"><font size="4">WAN
replication would be switched from between ServerB and
ServerC to between ServerA and ServerC,<br>
and afterwards ServerB would mount Layer5 LVM, Layer6
Filesystem and Layer7 Applications+VMs.</font></font></font><br>
Then ServerB would be the only server to write data, and
ServerA would send data to ServerC...<br>
<br>
Do you think we are bound to have any corruption in the above
scenario, <br>
if we make sure that Layer5 LVM and the above Layers will
never be mounted on more that one servers at a time?<br>
<br>
Thank you, <br>
<br>
Panos.</font></font></font><font size="4" face="monospace"><font
size="4" face="monospace"><font size="4" face="monospace"><br>
<br>
</font></font></font>
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