Prior to Oracle Database 12c, an ASM instance ran on every node in the cluster and ASM Cluster File System (ACFS) Service on a node connected to the local ASM instance running on the same host to fetch the required metadata. If the ASM instance on a node were to fail, then ACFS file systems could no longer be accessed on that node.

With introduction of Flex ASM in Oracle 12c, hard dependency between ASM and its clients has been relaxed and only a smaller number of ASM instances need run on a subset of servers in a cluster. In such a scenario, in order to make ACFS services available on nodes without an ASM instance, a new instance type has been introduced by Flex ASM: the ASM-proxy instance which works on behalf of a real ASM instance. ASM Proxy instance fetches the metadata about ACFS volumes and file systems from an ASM instance and caches it. If ASM instance is not available locally, ASM proxy instance connects to other ASM instances over the network to fetch the metadata. Additionally, if the local ASM instance fails, then ASM proxy instance can failover to another surviving ASM instance on a different server resulting in uninterrupted availability of shared storage and ACFS file systems.

Whenever IO needs to be performed on an ACFS, the ASM-Proxy instance passes on the extent map and disk list information to the ADVM driver. Subsequently, this metadata is cached by the ADVM driver. ADVM directs all the ACFS IOs to a specific ASM disk group disk (disks) location, including any mirrored extent updates. In other words, all ACFS IOs are written through the ADVM OS Kernel driver directly to storage. No IOs are delivered through the ASM proxy or ASM instance.

Which nodes can host ASM-Proxy instance?

ASM-Proxy instance only needs to run in the clusters employing Flex ASM on the nodes where access to ACFS is required. Whereas ASM-Proxy instance can run on any node in a standard cluster, only Hub nodes in a Flex cluster can host it (Fig. 1). It can run on the same node as ASM instance or on a different node. It can be shut down when ACFS is not running.
Which clusters use the ASM proxy instance

Fig. 1

The ASM Proxy instance has:

  • INSTANCE_TYPE initialization parameter set to ASMPROXY
  • ORACLE_SID set to +APX<node number>.

In this article, I will demonstrate that with Flex ASM:

  • Metadata related to ACFS is cached in ASM-Proxy instance rather than ASM instance
  • ASM-Proxy instance obtains the metadata related to ACFS from:
    • An ASM instance running locally
    • An ASM instance running remotely if the local ASM instance is not running
  • Availability of ACFS on a node:
    • Requires that ASM proxy instance must be running on that node
    • Is not affected by the failure of the local ASM instance

For this demonstration, I have set up a two node 12.1.0.2c Flex Cluster (with Flex ASM).

Overview:

  • Create a Cloud File System Resource on DATA disk group.
  • Verify that:
    • All the ASM and ACFS-related resources are running on both the nodes
    • Metadata related to ACFS is cached in ASM-Proxy instance rather than ASM instance
    • ASM-Proxy instance obtains the metadata related to ACFS from ASM instance running locally
  • Verify that on stopping ASM on a node (host02):
    • The ASM-Proxy instance obtains the metadata related to ACFS from an ASM instance running remotely
    • Availability of ACFS on the node is not affected
  • Verify that on stopping ASM- Proxy instance on a node (host02), ACFS cannot be accessed on that node even if ASM instance is available.

Demonstration:

[root@host01 ~]# crsctl get cluster mode status
Cluster is running in "flex" mode

[root@host01 ~]# crsctl get node role status -all
Node 'host01' active role is 'hub'
Node 'host02' active role is 'hub'

ASMCMD> showclustermode
ASM cluster : Flex mode enabled
  • Create a Cloud File System Resource on DATA disk group:
    • Check that Proxy instance is not running presently
[root@host01 ~]# crsctl stat res ora.proxy_advm -t
CRS-2613: Could not find resource 'ora.proxy_advm'.
  • Create a volume VOL1 on DATA disk group
[grid@host01 root]$ asmcmd setattr -G DATA compatible.advm 12.1.0.0.0
[grid@host01 root]$ asmcmd volcreate -G DATA -s 200m VOL1
[grid@host01 root]$ asmcmd volinfo -G DATA VOL1
Diskgroup Name: DATA
         Volume Name: VOL1
         Volume Device: /dev/asm/vol1-104
         State: ENABLED
         Size (MB): 256
         Resize Unit (MB): 64
         Redundancy: MIRROR
         Stripe Columns: 8
         Stripe Width (K): 1024
         Usage: 
         Mountpath:
    • As soon as the volume is created, an ASM proxy instance is automatically started on both nodes.
[root@host01 ~]# crsctl stat res ora.proxy_advm -t
--------------------------------------------------------------------------------
Name           Target  State        Server                   State details       
--------------------------------------------------------------------------------
Local Resources
--------------------------------------------------------------------------------
ora.proxy_advm
               ONLINE  ONLINE       host01                   STABLE
               ONLINE  ONLINE       host02                   STABLE

[root@host01 ~]# ps -ef |grep pmon
grid      7209     1  0 14:28 ?        00:00:00 asm_pmon_+ASM1
grid     10076     1  0 14:34 ?        00:00:00 apx_pmon_+APX1
root     11297  7103  0 14:37 pts/1    00:00:00 grep pmon

[root@host02 ~]# ps -ef |grep pmon
grid     13901     1  0 14:33 ?        00:00:00 apx_pmon_+APX2
root     15113 12648  0 14:37 pts/3    00:00:00 grep pmon
grid     16229     1  0 13:13 ?        00:00:00 asm_pmon_+ASM2
grid     20548     1  0 13:16 ?        00:00:00 mdb_pmon_-MGMTDB
    • Create an ACFS File System on the newly created volume VOL1
[root@host01 ~]# mkfs -t acfs /dev/asm/vol1-104
mkfs.acfs: version = 12.1.0.2.0
mkfs.acfs: on-disk version = 39.0
mkfs.acfs: volume = /dev/asm/vol1-104
mkfs.acfs: volume size = 268435456 ( 256.00 MB )
mkfs.acfs: Format complete.
    • Create Corresponding Mount Points on both nodes
[root@host01 ~]# mkdir -p /mnt/acfsmounts/acfs1
[root@host02 ~]# mkdir -p /mnt/acfsmounts/acfs1
    • Configure and start Cloud File System Resource on the volume device VOL1 with the mount point /mnt/acfsmounts/acfs1
[root@host01 ~]# srvctl add filesystem -path /mnt/acfsmounts/acfs1 -device /dev/asm/vol1-104
[root@host01 ~]# srvctl start filesystem -d /dev/asm/vol1-104
[root@host01 ~]# srvctl status filesystem -device /dev/asm/vol1-104
ACFS file system /mnt/acfsmounts/acfs1 is mounted on nodes host01,host02
    • Verify the Cloud File System Resource by creating a small text file created on it from host01 and then accessing it successfully from host02
[root@host01 ~]# echo “Test File on ACFS” > /mnt/acfsmounts/acfs1/testfile.txt
[root@host02 asm]# cat /mnt/acfsmounts/acfs1/testfile.txt
Test File on ACFS
  • Verify that All the ASM and ACFS-related resources are running on both nodes
 [root@host01 ~]#  crsctl stat res ora.asm ora.DATA.dg ora.DATA.VOL1.advm ora.data.vol1.acfs  -t
--------------------------------------------------------------------------------
Name           Target  State        Server                   State details       
--------------------------------------------------------------------------------
Local Resources
--------------------------------------------------------------------------------
ora.DATA.VOL1.advm
               ONLINE  ONLINE       host01                   Volume device /dev/a
                                                             sm/vol1-104 is onlin
                                                             e,STABLE
               ONLINE  ONLINE       host02                   Volume device /dev/a
                                                             sm/vol1-104 is onlin
                                                             e,STABLE
ora.DATA.dg
               ONLINE  ONLINE       host01                   STABLE
               ONLINE  ONLINE       host02                   STABLE
ora.asm
               ONLINE  ONLINE       host01                   Started,STABLE
               ONLINE  ONLINE       host02                   Started,STABLE
ora.data.vol1.acfs
               ONLINE  ONLINE       host01                   mounted on /mnt/acfs
                                                             mounts/acfs1,STABLE
               ONLINE  ONLINE       host02                   mounted on /mnt/acfs
                                                             mounts/acfs1,STABLE
  • Verify that Metadata for ACFS is cached in not cached in ASM instance
+ASM1>sho parameter instance_name
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
instance_name                        string      +ASM1

+ASM1> select name, state from v$asm_diskgroup;
NAME                           STATE
------------------------------ -----------
DATA                           MOUNTED

+ASM1>select fs_name, vol_device from v$ASM_ACFSVOLUMES; 
no rows selected

+ASM1>select fs_name, state from v$asm_filesystem;
no rows selected

+ASM1>select volume_name, volume_device, mountpath from v$asm_volume;
 
VOLUME_NAM VOLUME_DEVICE        MOUNTPATH
---------- -------------------- -------------------------
VOL1       /dev/asm/vol1-104    /mnt/acfsmounts/acfs1
  • Verify that Metadata for ACFS is cached in ASM-Proxy instance:
[grid@host01 ~]$ cat /etc/oratab | grep APX
+APX1:/u01/app/12.1.0/grid:N            # line added by Agent
[grid@host01 ~]# ps -ef |grep pmon
grid      8341     1  0 12:10 ?        00:00:00 asm_pmon_+ASM1
grid     10072     1  0 12:12 ?        00:00:00 apx_pmon_+APX1
grid     10752     1  0 12:13 ?        00:00:00 mdb_pmon_-MGMTDB
root     19167  7644  0 12:22 pts/1    00:00:00 grep pmon

+APX1> sho parameter instance_type
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
instance_type                        string      ASMPROXY

+APX1> sho parameter instance_name
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
instance_name                        string      +APX1
 
+APX1> select name, state from v$asm_diskgroup;
NAME                           STATE
------------------------------ -----------
DATA                           CONNECTED

+APX1>select fs_name, vol_device from v$ASM_ACFSVOLUMES;
FS_NAME                        VOL_DEVICE
------------------------------ --------------------
/mnt/acfsmounts/acfs1          /dev/asm/vol1-104

+APX1>select fs_name, state from v$asm_filesystem;
FS_NAME                        STATE
------------------------------ -------------
/mnt/acfsmounts/acfs1          AVAILABLE

+APX1>select volume_name, volume_device, mountpath from v$asm_volume;
 
VOLUME_NAM VOLUME_DEVICE        MOUNTPATH
---------- -------------------- -------------------------
VOL1       /dev/asm/vol1-104    /mnt/acfsmounts/acfs1
  • Verify that both the ASM-Proxy instances obtain the metadata related to ACFS from ASM instance running locally:
+ASM1> SELECT DISTINCT 
    i.instance_name asm_instance_name, 
    i.host_name asm_host_name, 
    c.instance_name client_instance_name, 
    c.status
  FROM gv$instance i, gv$asm_client c
 WHERE i.inst_id = c.inst_id;
ASM_INSTANCE_NAM ASM_HOST_NAME        CLIENT_INSTANCE_NAME STATUS
---------------- -------------------- -------------------- ------------
+ASM1            host01.example.com   +APX1                CONNECTED
+ASM1            host01.example.com   +ASM1                CONNECTED
+ASM2            host02.example.com   +APX2                CONNECTED
  • Verify that on stopping ASM on a node (host02),
    • ASM-Proxy instance obtains the metadata related to ACFS from an ASM instance running remotely
    • Availability of ACFS on the node is not affected
 [root@host01 ~]# srvctl stop asm -n host02

PRCR-1014 : Failed to stop resource ora.asm
PRCR-1065 : Failed to stop resource ora.asm
CRS-2529: Unable to act on 'ora.asm' because that would require stopping or relocating 'ora.DATA.dg', but the force option was not specified

[root@host01 ~]# srvctl stop asm -n host02 -f
[root@host01 ~]# srvctl status asm
ASM is running on host01
+ASM1> SELECT DISTINCT 
    i.instance_name asm_instance_name, 
    i.host_name asm_host_name, 
    c.instance_name client_instance_name, 
    c.status
  FROM gv$instance i, gv$asm_client c
 WHERE i.inst_id = c.inst_id;  
ASM_INSTANCE_NAM ASM_HOST_NAME        CLIENT_INSTANCE_NAME STATUS
---------------- -------------------- -------------------- ------------
+ASM1            host01.example.com   +APX1                CONNECTED
+ASM1            host01.example.com   +APX2                CONNECTED
+ASM1            host01.example.com   +ASM1                CONNECTED

[root@host01 ~]# crsctl stat res ora.asm ora.DATA.dg ora.DATA.VOL1.advm ora.data.vol1.acfs  -t
--------------------------------------------------------------------------------
Name           Target  State        Server                   State details       
--------------------------------------------------------------------------------
Local Resources
--------------------------------------------------------------------------------
ora.DATA.VOL1.advm
               ONLINE  ONLINE       host01                   Volume device /dev/a
                                                             sm/vol1-104 is onlin
                                                             e,STABLE
               ONLINE  ONLINE       host02                   Volume device /dev/a
                                                             sm/vol1-104 is onlin
                                                             e,STABLE
ora.DATA.dg
               ONLINE  ONLINE       host01                   STABLE
               OFFLINE OFFLINE      host02                   STABLE
ora.data.vol1.acfs
               ONLINE  ONLINE       host01                   mounted on /mnt/acfs
                                                             mounts/acfs1,STABLE
               ONLINE  ONLINE       host02                   mounted on /mnt/acfs
                                                             mounts/acfs1,STABLE
--------------------------------------------------------------------------------
Cluster Resources
--------------------------------------------------------------------------------
ora.asm
      1        ONLINE  ONLINE       host01                   Started,STABLE
      2        OFFLINE OFFLINE                               Instance Shutdown,ST
                                                             ABLE
--------------------------------------------------------------------------------
  • Verify that on stopping ASM- Proxy instance on a node (host02), ACFS cannot be accessed on that node even though ASM instance is present:
 [root@host01 ~]# srvctl start asm -n host02

[root@host01 ~]# srvctl stop asm -proxy -n host02
PRCR-1014 : Failed to stop resource ora.proxy_advm
PRCR-1065 : Failed to stop resource ora.proxy_advm
CRS-2529: Unable to act on 'ora.proxy_advm' because that would require stopping or relocating 'ora.DATA.VOL1.advm', but the force option was not specified

[root@host01 ~]# srvctl stop asm -proxy -n host02 -f
[root@host01 ~]# crsctl stat res ora.asm ora.DATA.dg ora.DATA.VOL1.advm ora.data.vol1.acfs  -t
--------------------------------------------------------------------------------
Name           Target  State        Server                   State details       
--------------------------------------------------------------------------------
Local Resources
--------------------------------------------------------------------------------
ora.DATA.VOL1.advm
               ONLINE  ONLINE       host01                   Volume device /dev/a
                                                             sm/vol1-104 is onlin
                                                             e,STABLE
               OFFLINE OFFLINE      host02                   Volume device /dev/a
                                                             sm/vol1-104 is offli
                                                             ne,STABLE
ora.DATA.dg
               ONLINE  ONLINE       host01                   STABLE
               ONLINE  ONLINE       host02                   STABLE
ora.data.vol1.acfs
               ONLINE  ONLINE       host01                   mounted on /mnt/acfs
                                                             mounts/acfs1,STABLE
               OFFLINE OFFLINE      host02                   volume /mnt/acfsmoun
                                                             ts/acfs1 is unmounte
                                                             d,STABLE
--------------------------------------------------------------------------------
Cluster Resources
--------------------------------------------------------------------------------
ora.asm
      1        ONLINE  ONLINE       host01                   Started,STABLE
      2        ONLINE  ONLINE       host02                   Started,STABLE
---------------------------------------------------------------------------------

Thus in a flex cluster, all metadata about ACFS is cached in ASM-Proxy instance. Also, availability of ACFS Volume and ACFS on a node is dependent on availability of an ASM–Proxy instance only on the node irrespective of the status of local ASM instance.

Summary

  • In a cluster with an ASM instance running on every node:
    • Metadata related to ACFS is cached in the ASM instance
    • Failure of the local ASM instance disrupts the availability of ACFS on that node
  • A new instance type has been introduced by Flex ASM – the ASM proxy instance, which gets metadata information from ASM instance on behalf of ACFS.
  • In a cluster with flex ASM
    • ASM instances run on a subset of nodes
    • Metadata related to ACFS is cached in the ASM-Proxy instance rather than the ASM instance
    • The ASM-Proxy instance obtains the metadata related to ACFS from the ASM instance running locally / remotely
    • Availability of ACFS on a node is dependent on availability of ASM–Proxy instance only irrespective of the status of local ASM instance.

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