[DRBD-user] DRBD 9 auto-promote not changing role to Primary, but is writable

[Philipp Reisner]

Hi,

from top of my head ZFS is special in that sense that it opens the backing
device only for a short amount of time. 

I mean it does the eqivalent of an open(2) call on the backend block device
and than very soon after that does the equivalent of a close(2).

All other linux file systems open(2) it during mount and keep it
open until unmount. Which seems pretty logical.

DRBD's auto-promote relies on open/close calls. In other words, if you
put ZFS on top of DRBD, do not use auto-promote. Use manual promote.

It is nothing we can fix on DRBD's side. This should be fixed in ZFS.

best regards,
 Phil


Am Mittwoch, 13. November 2019, 14:08:37 CST schrieb Doug Cahill:
> I'm configuring a two node setup with drbd 9.0.20-1 on CentOS 7
> (3.10.0-957.1.3.el7.x86_64) with a single resource backed by an SSDs.  I've
> explicitly enabled auto-promote in my resource configuration to use this
> feature.
> 
> The drbd device is being used in a single-primary configuration as a zpool
> SLOG device.  The zpool is only ever imported on one node at a time and the
> import is successful during cluster failover events between nodes.  I
> confirmed through zdb that the zpool includes the configured drbd device
> path.
> 
> My concern is that the drbdadm status output shows the Role of the drbd
> resource as "Secondary" on both sides.  The documentations reads that the
> drbd resource will be auto promoted to primary when it is opened for
> writing.
> 
> drbdadm status
> r0 role:Secondary
>   disk:UpToDate
>   dccdx0 role:Secondary
>     peer-disk:UpToDate
> 
> My device should be opened for writing when the zpool is imported.  I've
> even tested writing to the pool with "dd oflag=sync" to force sync writes
> to the SLOG which is the drbd resource.  The drbd device never changes the
> reported state but it appears to be writable.
> 
> Have I misconfigured my drbd resource for an auto-promote configuration
> and/or is my use case to obscure for auto-promote to detect the device is
> being written to when used in a zpool?
> 
> =========== /etc/drbd.d/r0.res
> resource r0 {
>     disk "/dev/disk/by-path/pci-0000:18:00.0-scsi-0:0:2:0-part1";
>     meta-disk internal;
>     device minor 0;
> 
>     on dccdx0 {
>         address 192.0.2.10:7000;
>     }
> 
>     on dccdx1 {
>         address 192.0.2.20:7000;
>     }
> 
>     disk {
>         read-balancing when-congested-remote;
>         no-disk-flushes;
>         no-md-flushes;
>         # al-updates no; # turn off al-tracking; requires full sync on crash
> c-fill-target 4M;
>         resync-rate 500M;
>         c-max-rate 1000M;
>         c-min-rate 700M;
>     }
> 
>     net {
>         sndbuf-size 10M;
>         rcvbuf-size 10M;
>         max-buffers 20000;
>         fencing resource-and-stonith;
>     }
> }
> 
> -Doug