ASM 12c A powerful framework for storage management

 

ASM 12c

A powerful framework for storage management

INTRODUCTION

Oracle Automatic Storage Management (ASM) is a well-known, largely used multi-platform volume manager and file system, designed for single-instance and clustered environment. 

Developed for managing Oracle database files with optimal performance and native data protection, simplifying the storage management; nowadays ASM includes several functionalities for general-purpose files too.

This article focuses on the architecture and characteristics of the version 12c, where great changes and enhancements of pre-existing capabilities have been introduced by Oracle.

Dedicated sections explaining how Oracle has leveraged ASM within the Oracle Engineered Systems complete the paper.

👉ASM 12c Instance Architecture Diagram👈

Below are highlighted the functionalities and the main background components associated to an ASM instance. 

It is important to notice how starting from Oracle 12c a database can run within ASM Disk Groups or on top of ASM Cluster file systems (ACFS).

👉Overview ASM options available in Oracle 12c.👈

👉ASM 12c Multi-Nodes Architecture Diagram👈

In a Multi-node cluster environment, ASM 12c is now available in two configurations:

• 11gR2 like: with one ASM instance on each Grid Infrastructure node.

• Flex ASM: a new concept, which leverages the architecture availability and performance of the cluster; removing the 1:1 hard dependency between cluster node and local ASM instance. 
• With Flex ASM only few nodes of the cluster run an ASM instance, (the default cardinality is 3) and the database instances communicate with ASM in two possible way: locally or over the ASM Network. 
• In case of failure of one ASM instance, the databases automatically and transparently reconnect to another surviving instance on the cluster. 
• This major architectural change required the introduction of two new cluster resources, ASM-Listener for supporting remote client connections and ADVM-Proxy, which permits the access to the ACFS layer. 
• In case of wide cluster installation, Flex ASM enhances the performance and the scalability of the Grid Infrastructure, reducing the amount of network traffic generated between ASM instances.

 

Below two graphical representations of the same Oracle cluster; on the first drawing ASM is configured with pre-12c setup, on the second one Flex ASM is in use.

Flex ASM architecture

ASM 12c NEW FEATURES

The table below summarizes the list of new functionalities introduced on ASM 12c R1

Feature	Definition
Filter Driver	Filter Driver (Oracle ASMFD) is a kernel module that resides in the I/O path of the Oracle ASM disks used to validate write I/O requests to Oracle ASM disks, eliminates accidental overwrites of Oracle ASM disks that would cause corruption. For example, the Oracle ASM Filter Driver filters out all non-Oracle I/Os which could cause accidental overwrites.
General ASM Enhancements	–       Oracle ASM now replicates physically addressed metadata, such as the disk header and allocation tables, within each disk, offering a better protection against bad block disk sectors and external corruptions. –       Increased storage limits: ASM can manage up to 511 disk groups and a maximum disk size of 32 PB. –       New REPLACE clause on the ALTER DISKGROUP statement.
Disk Scrubbing	Disk scrubbing checks logical data corruptions and repairs the corruptions automatically in normal and high redundancy disks groups. This process automatically starts during rebalance operations or the administrator can trigger it.
Disk Resync Enhancements	It enables fast recovery from instance failure and faster resyncs performance. Multiple disks can be brought online simultaneously. Checkpoint functionality enables to resume from the point where the process was interrupted.
Even Read For Disk Groups	If ASM mirroring is in use, each I/O request submitted to the system can be satisfied by more than one disk. With this feature, each request to read is sent to the least loaded of the possible source disks.
ASM Rebalance Enhancements	The rebalance operation has been improved in term of scalability, performance, and reliability; supporting concurrent operations on multiple disk groups in a single instance.  In this version, it has been enhanced also the support for thin provisioning, user-data validation, and error handling.
ASM Password File in a Disk Group	ASM Password file is now stored within the ASM disk group.
Access Control Enhancements on Windows	It is now possible to use access control to separate roles in Windows environments. With Oracle Database services running as users rather than Local System, the Oracle ASM access control feature is enabled to support role separation on Windows.
Rolling Migration Framework for ASM One-off Patches	This feature enhances the rolling migration framework to apply oneoff patches released for ASM in a rolling manner, without affecting the overall availability of the cluster or the database
Updated Key Management Framework	This feature updates Oracle key management commands to unify the key management application programming interface (API) layer. The updated key management framework makes interacting with keys in the wallet easier and adds new key metadata that describes how the keys are being used.

 

👉ASM 12c Client Cluster👈

One more ASM functionality explored but still in phase of development and therefore not really documented by Oracle, is ASM Client Cluster.

Designed to host applications requiring cluster functionalities (monitoring, restart and failover capabilities), without the need to provision local shared storage.

The ASM Client Cluster installation is available as configuration option of the Grid Infrastructure binaries, starting from version 12.1.0.2.1 with Oct. 2014 GI PSU.

The use of ASM Client Cluster imposes the following pre-requisites and limitations:

• The existence of an ASM Server Cluster version 12.1.0.2.1 with Oct. 2014 GI PSU, configured with the GNS server with or without zone delegation.
• The ASM Server Cluster becomes aware of the ASM Client Cluster by importing an ad hoc XML configuration containing all details.
• The ASM Client Cluster uses the OCR, Voting Files and Password File of the ASM Server Cluster.
• ASM Client Cluster communicates with the ASM Server Cluster over the ASM Network.
• ASM Server Cluster provides remote shared storage to ASM Client Cluster.

 

ACFS NEW FEATURES

In Oracle 12c the Automatic Storage Management Cluster File System supports more and more types of files, offering advanced functionalities like snapshot, replication, encryption, ACL and tagging.  It is also important to highlight that this cluster file system comply with the POSIX standards of Linux/UNIX and with the Windows standards.

Access to ACFS from outside the Grid Infrastructure cluster is granted by NFS protocol; the NFS export can be registered as clusterware resource becoming available from any of the cluster nodes (HANFS).

Here is an exhaustive list of files supported by ACFS: executables, trace files, logs, application reports, BFILEs, configuration files, video, audio, text, images, engineering drawings, general-purpose and Oracle database files.

The major change, introduced in this version of ACFS, is definitely the capability and support to host Oracle database files; granting access to a set of functionalities that in the past were restricted to customer files only. Among them, the most important is the snapshot image, which has been fully integrated with the database Multitenant architecture, allowing cloning entire Pluggable databases in few seconds, independently from the size and in space efficient way using copy-on-write technology.

The snapshots are created and immediately available in the “<FS_mount_point>.ASFS/snaps” directory, and can be generated and later converted from read-only to read/write and vice versa. In addition, ACFS supports nested snapshots.

 

Example of ACFS snapshot copy:

-- Create a read/write Snapshot copy

[grid@oel6srv02 bin]$ acfsutil snap create -w cloudfs_snap /cloudfs

-- Display Snapshot Info
[grid@oel6srv02 ~]$ acfsutil snap info cloudfs_snap /cloudfs

snapshot name:               cloudfs_snap
RO snapshot or RW snapshot:  RW
parent name:                 /cloudfs
snapshot creation time:      Wed May 27 16:54:53 2015

-- Display specific file info 
[grid@oel6srv02 ~]$ acfsutil info file /cloudfs/scripts/utl_env/NEW_SESSION.SQL
/cloudfs/scripts/utl_env/NEW_SESSION.SQL
flags:        File
inode:        42
owner:        oracle
group:        oinstall
size:         684
allocated:    4096
hardlinks:    1
device index: 1
major, minor: 251,91137
access time:  Wed May 27 10:34:18 2013
modify time:  Wed May 27 10:34:18 2013
change time:  Wed May 27 10:34:18 2013
extents:
-offset ----length | -dev --------offset
0       4096 |    1     1496457216
extent count: 1

--Convert the snapshot from Read/Write to Read-only
acfsutil snap convert -r cloudfs_snap /cloudfs

 --Drop the snapshot 
[grid@oel6srv02 ~]$ acfsutil snap delete cloudfs_snap /cloudfs

Example of Pluggable database cloned using ACFS snapshot copy List of requirements that must be met to use ACFS SNAPSHOT COPY clause:

• All pluggable database files of the source PDB must be stored on ACFS.

 

 

• The source PDB cannot be in a remote CDB.

 

 

• The source PDB must be in read-only mode.

 

 

• Dropping the parent PDB with the including datafiles clause, does not automatically remove the snapshot dependencies, manual intervention is required.

 

 

SQL> CREATE PLUGGABLE DATABASE pt02 FROM ppq01
2  FILE_NAME_CONVERT = ('/u02/oradata/CDB4/PPQ01/',
3                       '/u02/oradata/CDB4/PT02/')
4  SNAPSHOT COPY;
Pluggable database created.
Elapsed: 00:00:13.70

The PDB snapshot copy imposes few restrictions among which the source database opened in read-only. This requirement prevents the implementation on most of the production environments where the database must remain available in read/write 24h/7. For this reason, ACFS for database files is particularly recommended on test and development where flexibility, speed and space efficiency of the clones are key factors for achieving high productive environment.

Graphical representation of how efficiently create and maintain a Test & Development database environment:

Conclusion

Oracle Automatic Storage Management 12c is a single integrated solution, designed to manage database files and general-purpose data under different hardware and software configurations. 

The adoption of ASM and ACFS not only eliminates the need for third party volume managers and file systems, but also simplifies the storage management offering the best I/O performance, enforcing Oracle best practices. 

In addition, ASM 12c with the Flex ASM setup removes previous important architecture limitations:

• Availability: the hard dependency between the local ASM and database instance, was a single point of failure. In fact, without Flex ASM, the failure of the ASM instance causes the crash of all local database instances.
• Performance: Flex ASM reduces the network traffic generated among the ASM instances, leveraging the architecture scalability; and it is easier and faster to keep the ASM metadata synchronized across large clusters. Finally yet importantly, only few nodes of the cluster have to support the burden of an ASM instance, leaving additional resources to application processing.

 

Oracle ASM offers a large set of configurations and options; it is now our duty to understand case-by-case, when it is relevant to use one setup or another, with the aim to maximize performance, availability and flexibility of the infrastructure.