Using autofs with Oracle Recovery Manager (RMAN) and dNFS

Background

This week I was asked an interesting question can Oracle dNFS and Oracle Recovery Manager (RMAN) use auto mounts, not knowing the answer I thought I better find out.

What is Autofs ?

Autofs, also known as automounter mounts filesystems on-demand when they are accessed rather than maintaining the mounts all the time.

The automounter umounts file systems after a period of inactivity on the mount freeing up system resources, the default timeout is 300 seconds but this can be changed, as I will demonstrate.

Installation

Install the autofs package

[oracle@z-rac1 ~]$ sudo yum install autofs

This will create a number of file in /etc which we can see using ls -ls /etc/auto* e.g.

[oracle@z-rac1 ~]$ ls -l /etc/auto*
-rw-r--r--. 1 root root 15137 Mar 30 11:37 /etc/autofs.conf
-rw-------. 1 root root   232 Mar 30 11:37 /etc/autofs_ldap_auth.conf
-rw-r--r--. 1 root root   795 Mar 30 11:37 /etc/auto.master
-rw-r--r--. 1 root root   524 Mar 30 11:37 /etc/auto.misc
-rwxr-xr-x. 1 root root  1260 Mar 30 11:37 /etc/auto.net
-rwxr-xr-x. 1 root root   687 Mar 30 11:37 /etc/auto.smb

The /etc/auto.master is the main configuration file and includes example mapping between mount points and a map file contains definitions of the remote filesystems which can be mounted.

Create Automounter Map

We can now create our automounter configuration for our NFS mount point and required timeout, note the file must end in .autofs otherwise it will be ignored.

[oracle@z-rac1 ~]$ sudo vi /etc/auto.master.d/fbnfs.autofs

Below is my file for my NFS mount of /mnt/orabkup referencing a map file call auto.fbnfs with a timeout of 180.

/mnt/orabkup    /etc/auto.fbnfs  --timeout=180

Create Map File

We now need to create the map file, here I have provided my mounting options, the Pure Storage FlashBlade IP address and NFS share name.

FlashBlade NFS share
[oracle@z-rac1 ~]$ sudo vi /etc/auto.fbnfs

This file can contain multiple mount points and shares in required, just add additional lines.

DEMO -fstype=nfs, rw, soft, intr 192.168.4.100:/z-oracle_orabkup
ORCL -fstype=nfs, rw, soft, intr 192.168.4.100:/z-oracle_orabkup2

Start autofs Service

Use sudo to start the autofs service with systemctl enable –now autofs

[oracle@z-rac1 ~]$ sudo systemctl enable --now autofs
Created symlink from /etc/systemd/system/multi-user.target.wants/autofs.service to /usr/lib/systemd/system/autofs.service.

Check the service using systemctl status autofs

[oracle@z-rac1 ~]$ sudo systemctl status autofs
autofs.service - Automounts filesystems on demand
   Loaded: loaded (/usr/lib/systemd/system/autofs.service; enabled; vendor preset: disabled)
   Active: active (running) since Fri 2021-05-07 11:17:43 BST; 2min 1s ago
 Main PID: 27080 (automount)
    Tasks: 6
   CGroup: /system.slice/autofs.service
           └─27080 /usr/sbin/automount --systemd-service --dont-check-daemon

May 07 11:17:43 z-rac1.uklab.purestorage.com systemd[1]: Starting Automounts filesystems on demand...
May 07 11:17:43 z-rac1.uklab.purestorage.com systemd[1]: Started Automounts filesystems on demand.

Access Mount Point

Before we try and access the mount point, let’s check the mount point.

[oracle@z-rac1 ~]$ df -h /mnt/orabkup
Filesystem       Size  Used Avail Use% Mounted on
/etc/auto.fbnfs     0     0     0    - /mnt/orabkup

Shows we are using /etc/autofs.fbnfs and no NFS shares are mounted, if perform an ls we can see no results.

[oracle@z-rac1 ~]$ cd /mnt/orabkup/
[oracle@z-rac1 orabkup]$ ls -l
total 0

Now let’s move into an auto mount directory and repeat.

[oracle@z-rac2 orabkup]$ cd ORCL
[oracle@z-rac2 ORCL]$ ls -l
total 369087576
-rw-r----- 1 oracle dba      34358697984 Nov 18 09:58 data_D-ORCL_I-1568428048_TS-IOPS_FNO-10_g5vfqpb8
-rw-r----- 1 oracle dba      34358697984 Dec 15 15:54 data_D-ORCL_I-1568428048_TS-IOPS_FNO-10_glvi58m8
...

And again check df -h

[oracle@z-rac2 ORCL]$ df -h
Filesystem                        Size  Used Avail Use% Mounted on
192.168.4.100:/z-oracle_orabkup1   10T  384G  9.7T   4% /mnt/orabkup/ORCL

If we repeat for our DEMO mount point we can see it also get auto mounted.

[oracle@z-rac2 DEMO]$ df -h
192.168.4.100:/z-oracle_orabkup1   10T  446G  9.6T   5% /mnt/orabkup/ORCL
192.168.4.100:/z-oracle_orabkup    10T  7.8T  2.3T  78% /mnt/orabkup/DEMO

Auto unmount

Now let’s check the autofs unmount is working.

[oracle@z-rac1 ~]$ date; df -h | grep ORCL
Fri  7 May 15:40:25 BST 2021
192.168.4.100:/z-oracle_orabkup1   10T  2.7T  7.4T  27% /mnt/orabkup/ORCL
[oracle@z-rac1 ~]$

And wait…

[oracle@z-rac1 ~]$ date; df -h | grep ORCL
Fri  7 May 15:50:51 BST 2021
[oracle@z-rac1 ~]$ 

And as if my magic my mount has disappeared.

Oracle Recovery Manager (RMAN)

Ok, what about RMAN, can that use the automounter ?

Good news, when Oracle RMAN process tries to write to the NFS mount point autofs detects the access and mounts the NFS share automatically as expected.

[oracle@z-rac1 ~]$ df -h
Filesystem                        Size  Used Avail Use% Mounted on
192.168.4.100:/z-oracle_orabkup1   10T  125G  9.9T   2% /mnt/orabkup/ORCL 

Oracle Direct NFS (dNFS)

So can Oracle dNFS work with autofs mounted NFS filesystems, without an /etc/fstab entry ?

The answer is yes, Oracle can use the /etc/mtab -> /proc/self/mounts to see the active NFS shared mounted by autofs and use it.

[oracle@z-rac1 ORCL]$ cat /proc/self/mounts | grep ORCL
192.168.4.100:/z-oracle_orabkup1 /mnt/orabkup/ORCL nfs rw,relatime,vers=3,rsize=524288,wsize=524288,namlen=255,soft,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=192.168.4.100,mountvers=3,mountport=2049,mountproto=udp,local_lock=none,addr=192.168.4.100 0 0

Using some of the dNFS views I have previously blogger about to confirm Oracle dNFS is is use.

$ cat $ORACLE_HOME/dbs/oranfstab

server: flashblade1
local: 192.168.4.2 path: 192.168.4.100
local: 192.168.5.2 path: 192.168.5.100
local: 192.168.6.2 path: 192.168.6.100
local: 192.168.7.2 path: 192.168.7.100
nfs_version: nfsv3
export: /z-oracle_orabkup  mount: /mnt/orabkup/DEMO
export: /z-oracle_orabkup1 mount: /mnt/orabkup/ORCL
SQL> SELECT distinct svrname, path FROM v$dnfs_channels;
SVRNAME          PATH
---------------- -----
flashblade1      192.168.4.100
flashblade1      192.168.5.100
flashblade1      192.168.6.100
flashblade1      192.168.7.100
SQL> SELECT svrname, dirname, wtmax, rtmax FROM v$dnfs_servers;

SVRNAME      DIRNAME             WTMAX  RTMAX
------------ ------------------  ------ ------
flashblade1  /z-oracle_orabkup1  524288	524288

Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.10.0.0.0

Summary

In this post I have shown:

  • We can use autofs to automatically mount and unmount linux filesystems.
  • Autofs can detect Oracle RMAN requesting access to an NFS filesystem and mount the share on demand.
  • Autofs can detect that the NFS filesystem is no longer required by RMAN and unmount the NFS share.
  • Oracle Direct NFS detects RMAN is using a NFS share configured for use with dNFS and uses it.

Hope you found the above useful and informative, if so follow my blog or me on Twitter using the button below.

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