postgresql on iscsi that refuses to start ... on server's boot - Redhat 7.1

Question

I installed a postgresql database on Redhat 7.1 and I decided to move the database on an ISCSI device (LUN) inside a logical volume, mounted at starting of the machine (xfs formatted). The mounting point is /var/lib/pgsql

At the boot of the server, postgresql.service is in failed status.

In messages.log:

systemd: mounting /var/lib/pgsql
 starting PostgreSQL database server
 kernel sdv: unknown partition table
 sd 2:0:0:0: [sdb] attached SCSI disk
 xfs (dm-4): Mounting V4 Filesystem
 postgresql-check-db-dir: "/var/lib/pgsql/data" is missing or empty
 postgresql.service: control process exited, code=exited status=1
 Failed to start PostgreSQL database server.

When I'm logged on the server, if it try to start manually the database : systemctl start postgresql --> OK (and I don't lose any data, database is available)

I think it's a problem of order in the boot process : network service must be started, then iscsi, then lvm etc... So I tried to force dependencies on the /usr/lib/systemd/system/postgresql.service adding "After=lvm-pgscan.service iscsi.service" etc... but the result is the same :

failure in starting postgresql

systemd: Starting Remote File Systems (Pre)
systemd: Reached Remote File Systems (Pre)
systemd: mounting /var/lib/pgsql
systemd:  starting PostgreSQL database server
kernel sdb: unknown partition table
postgresql-check-db-dir: "/var/lib/pgsql/data" is missing or empty
kernel: xfs (dm-4): Mounting V4 Filesystem
postgresql.service: control process exited, code=exited status=1
Failed to start PostgreSQL database server.
Unit postgresql.service entered failed state
sd 2:0:0:0: [sdb] attached SCSI disk
starting LVM2 PV scan on device 8:16
kernel: xfs (dm-3): Ending clean mount
systemd: Mounted /var/lib/pgsql
Starting Remote File Systems
Reached target Remote File Systems

Any ideas?

Answer 1

To make sure PostgreSQL starts after iSCSI volume are mounted, do the following:

cat >/etc/systemd/system/postgresql.service <<EOF
.include /lib/systemd/system/postgresql.service
[Unit]
After=remote-fs.target
EOF

This works with an arbitrary service (MongoDB, MySQL...) and any kind of remote access (NFS, Samba...).

Answer 2

I have solved it on my server (RHEL 7.2) by editing /usr/lib/systemd/system/postgresql-9.5.service and adding After=remote-fs.target