OraNA :: Oracle News Aggregator

Some long-running ASM operations, like rebalance, drop disk, create/delete/resize file, cannot be described by a single record in the active change directory. For those operations ASM uses the Continuing Operations Directory (COD) - ASM file number 4. There is one COD per disk group.

If a process performing the long-running operation dies before completing it, a recovery process will look at the entry and either complete or rollback the operation. There are two types of continuing operations - background and rollback.

Background operation

A background operation is preformed by an ASM instance background process. It is done as part of (more...)

When ASM needs to make an atomic change to multiple metadata blocks, a log record is written into the Active Change Directory (ACD), which is ASM metadata file number 3. These log records are written in a single I/O.

ACD is divided into chunks (threads) and each running ASM instance has its own 42 MB chunk. When a disk group is created, a single chunk is allocated for the ACD. As more instances mount that disk group, the ACD grows (by 42 MB) to accommodate every running instance with its own ACD chunk.

The ACD components are:

• ACDC - ACD (more...)

ASM file number 2 - the disk directory - keeps track of all disks in the disk group. As disk groups are independent storage units, each disk group will have its own disk directory.

As far as ASM is concerned, the disk directory is just another file. It has its own entry in the file directory, it is mirrored as per the disk group redundancy policy and it grows as needed.

Each disk directory entry maintains the following information:

• Disk number
• Disk state
• ASM disk name (this can differ from the disk's OS name)
• Fail group name
• Create time-stamp
• Failure time-stamp
• (more...)

ASM file number 1 - the file directory - keeps track of all files in the disk group. As disk groups are independent storage units, each will have its own file directory.

While this is an internal file, part of ASM metadata, it is managed like any other file in the disk group. It will have its own entry in the file directory, it will be mirrored in a normal and high redundancy disk group and will automatically grow to accommodate more files.

Each file directory entry maintains the following information:

• File size
• File block size
• File type 
• File redundancy level
• (more...)

Some ASM commands have the "force" option that allows the administrator to override a default behaviour. While some uses of the force option are perfectly safe and indeed required, some may render your disk group unusable. Let's have a closer look.

Mount force

The force option becomes a must when a disk group mount reports missing disks. This is one of the cases when it's safe and required to use the force option. Provided we are not missing too many disks, the mount force should succeed. Basically, at least one partner disk - from every disk partnership in the disk group - must be available.

(more...)