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Quorum disks in Exadata
An Exadata quarter rack has two database servers and three storage cells. In a typical setup, such a system would have three ASM disk groups, say DATA, RECO and DBFS_DG. Usually the disk group DATA...
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ASM data scrubbing
According toWikipedia, data scrubbing is “an error correction technique that uses a background task to periodically inspect main memory or storage for errors, and then correct detected errors using...
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Error count
This tiny Perl script might be used to report the error type and count for ASM disks in engineered systems, including Exadata. In those systems, the ASM uses griddisks, that are created from celldisks....
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The ASM password directory
Password file authentication for Oracle Database or ASM can work for both local and remote connections. In Oracle version 12c, the password files can reside in an ASM disk group. The ASM metadata...
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Tell me about your ASM
When diagnosing ASM issues, it helps to know a bit about the setup - disk group names and types, the state of disks, ASM instance initialisation parameters and if any rebalance operations are in...
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ASM metadata blocks
An ASM instance manages the metadata needed to make ASM files available to Oracle databases and other ASM clients. ASM metadata is stored in disk groups and organised in metadata structures. These...
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Partnership and Status Table
The Partnership and Status Table (PST) contains the information about all ASM disks in a disk group – disk number, disk status, partner disk number, heartbeat info and the failgroup info (11g and...
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Allocation Table
Every ASM disk contains at least one Allocation Table (AT) that describes the contents of the disk. The AT has one entry for every allocation unit (AU) on the disk. If an AU is allocated, the...
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Free Space Table
The ASM Free Space Table (FST) provides a summary of which allocation table blocks have free space. It contains an array of bit patterns indexed by allocation table block number. The table is used to...
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Physical metadata replication
Starting with version 12.1, ASM replicates the physically addressed metadata. This means that ASM maintains two copies of the disk header, the Free Space Table and the Allocation Table data. Note that...
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ASM version 12c is out
Oracle Database version 12c has been released, which means a brand new version of ASM is out! Notable new features are Flex ASM, proactive data validation and better handling of disk management...
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How many allocation units per file
This post is about the amount of space allocated to ASM based files.The smallest amount of space ASM allocates is an allocation unit (AU). The default AU size is 1 MB, except in Exadata where the...
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Auto disk management feature in Exadata
The automatic disk management feature is about automating ASM disk operations in an Exadata environment. The automation functionality applies to both planned actions (for example, deactivating...
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Identification of under-performing disks in Exadata
Starting with Exadata software version 11.2.3.2, an under-performing disk can be detected and removed from an active configuration. This feature applies to both hard disks and flash disks.About storage...
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Where is my data
Sometimes we want to know where exactly is a particular database block - on which ASM disk, in which allocation unit on that disk and in which block of that allocation unit. In this post I will show...
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When will my rebalance complete
This has to be one of the top ASM questions people ask me. But if you expect me to respond with a number of minutes, you will be disappointed. After all, ASM has given you an estimate, and you still...
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Exadata motherboard replacement
This photo story is about a motherboard replacement in an Exadata X2-2 database server (Sun Fire X4170 M2).While setting up a half rack Exadata system, we discovered a problem with the motherboard in...
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ASM in Exadata
ASM is a critical component of the Exadata software stack. It is also a bit different - compared to non-Exadata environments. It still manages your disk groups, but builds those with grid disks. It...
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ASM files number 12 and 254
The staleness directory (ASM file number 12) contains metadata to map the slots in the staleness registry to particular disks and ASM clients. The staleness registry (ASM file number 254) tracks...
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Find block in ASM
In the post Where is my data I have shown how to locate and extract an Oracle datafile block from ASM. To make things easier, I have now created a Perl script find_block.pl that automates the process -...
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