What will be the syntax of ASM filenames?
ASM filename syntax is given below
+diskgroup_name – Name of the diskgroup that contains this file
database_name – Name of the database that contains this file
datafile – Can be one among 20 different ASM file types
tag_name – corresponds to tablespace name for datafiles, groupnumber for redo log files
file_number – file_number in ASM instance is used to correlate filenames in database instance
incarnation_number – It is derived from the timestamp. IT is used to provide uniqueness
What is an incarnation number?
An incarnation number is a part of ASM filename syntax. It is derived from the time stamp. Once the file is created, its incarnation number doesn’t change.
What is the use of an incarnation number in Oracle ASM filename?
Incarnation number distinguishes between a new file that has been created using the same file number and another file that has been deleted
What is an oracle flex ASM?
Oracle flex ASM is a feature that enables an ASM instance to run on separate physical servers from the database servers this feature comes with 12C.In earlier releases Oracle used to have ASM instance on every physical node/server which runs ASM based databases on that node/server.
What If my ASM instance goes down? what will happen with my databases which are using the ASM?can we avoid this ?
If ASM instance goes down ,All the databases using ASM instance will also goes down and will only be open once ASM instance and its all disk group comes into mount stage.to avoid this situation we can use FLEX feature of ASM (12C onwards).
What is the use of asmadmin group on OS?
asmadmin is the operating system group that holds users who have sysasm database privilege. This privilege is needed for operations like mounting disk group, dismounting disk group, storage administration
What is the purpose of asmoper operating system group?
asmoper operating system group is used for users that have the privilege to startup and stop the oracle ASM instance. The database privilege for these users will be sysoper for asm
What is the difference between asmdba and asmoper groups?
The users belonging to asmdba group have sysdba database privilege at ASM level. This is the highest administrative privilege needed for oracle ASM. Whereas, asmoper is given sysoper privilege which is less than asmdba
What is ASM metadata and where is it present?
ASM metadata is the information that ASM uses to control the disk group.It is present within a disk groups.
What is an ASM metadata composed of?
An ASM metadata includes the following:
1) The disks that belong to a disk group
2) Amount of space available within a disk group
3) The filenames of the files within a disk group
4) The location of disk group datafile data extents
5) A redo log that records information about automatically changing data blocks
Can we change the Redundancy for Diskgroup after its creation?
No, we cannot modify the redundancy for Diskgroup once it has been created. To alter it we will be required to create a new Diskgroup and move the files to it. This can also be done by restoring full backup on the new Diskgroup.
Does ASM instance automatically rebalances and takes care of hot spots?
No. This is a myth and ASM does not do it. It will initiate automatic rebalance only when a new disk is added to Diskgroup or we drop a disk from existing Diskgroup.
What is ASMLIB?
ASMLIB is the support library for the ASM. ASMLIB allows an Oracle database using ASM more efficient and capable access to diskgroups. The purpose of ASMLIB, is to provide an alternative interface to identify and access block devices. Additionally, the ASMLIB API enables storage and operating system vendors to supply extended storage-related features.
What is SYSASM role?
Starting from Oracle 11g, SYSASM role can be used to administer the ASM instances. You can continue using SYSDBA role to connect to ASM but it will generate following warning messages at time of startup/shutdown, create Diskgroup/add disk, etc
WARNING: Deprecated privilege SYSDBA for command ‘STARTUP’
What is the best LUN size for ASM ?
There is no best size. In most cases the storage team will dictate to you based on their standardized LUN size. The ASM administrator merely has to communicate the ASM Best Practices and application characteristics to storage folks :
a)Need equally sized / performance LUNs
b) Minimum of 4 LUNs
c) The capacity requirement
d) The workload characteristic (random r/w, sequential r/w) & any response time SLA
Can my RDBMS and ASM instances run different versions?
Yes. ASM can be at a higher version or at lower version than its client databases. There’s two components of compatibility:
a) Software compatibility
b) Diskgroup compatibility attributes:
How do I backup my ASM instance?
There is no backup for ASM instance as ASM has no files to backup Unlike the database, ASM does require a controlfile type structure or any other external metadata to bootstrap itself. All the data ASM needs to startup is on on-disk structures (disk headers and other disk group metadata).