Common Log File System Series Of Steps

By separating the data into pieces and giving each piece a name, the data is easily isolated and identified.

It was introduced with Windows Server 2003 R2 and included in later Windows operating systems.

CLFS can be used for both data logging as well as for event logging.

CLFS is used by TxF and TxR to store transactional state changes before they commit a transaction.

Binary Log File(s) created from CLFS can not be viewed by any integrated Windows tool.

Common Log File System Series Of Steps

Contents Overview References External links Overview The job of CLFS, like any other transactional logging system, is to record a series of steps required for some action so that they can be either played back accurately in the future to commit the transaction to secondary storage or undone if required.

When the data will be flushed to stable media is controlled by built-in policies, but a CLFS client application can override that and force a flush.

CLFS allows for customizable log formats, expansion and truncation of logs according to defined policies, as well as simultaneous use by multiple client applications.

CLFS is able to store log files anywhere on the file system.

CLFS defines a device driver interface (DDI), via which physical storage system specific drivers plug into the CLFS API.

CLFS supports both dedicated logs, as well as multiplexed logs.

A dedicated log contains a single stream of log records whereas multiplexed log contain multiple streams, each stream for a different application.

Even though a multiplexed log has multiple streams, logs are flushed to the streams sequentially, in a single batch.

CLFS can allocate space for a set of log records ahead-of-time (before the logs are actually generated) to make sure the operation does not fail due to lack of storage space.

A log record in a CLFS stream is first placed to Log IO Block in a buffer in system memory.

On the storage device, a log contains a set of Containers, which are allocated contiguously, each containing multiple Log IO Blocks.

Each record is identified by a Log Sequence Number (LSN), an increasing 32-bit sequence number.

The LSN encodes the identifier of the container, the offset to the record and the identifier of the record - this information is used to access the log record subsequently.

However, the container identifiers are logical identifiers, they must be mapped to physical containers.

The mapping is done by CLFS itself.

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