[This is preliminary documentation and subject to change]

# About the Metabase History Feature

By marking each new metabase file with a unique version number and saving a copy of the file in the history folder, the metabase history feature automatically keeps track of metabase changes that are saved to disk. Each history file is then available for restoring the MetaBase.xml and MBSchema.xml files from history, editing the MetaBase.xml file while IIS is running, and for troubleshooting event log errors. The metabase history feature is enabled by default.

## History Folder

The history folder is a file system folder used to store versioned copies of the MetaBase.xml and MBSchema.xml files. The default location of the history folder is as follows:

`%windir%\system32\inetsrv\history`

The location and the name of MetaBase.xml can be changed via a Changing the Location and/or Name of MetaBase.xml. If the location of the MetaBase.xml file is changed, the history folder must be relocated relative to the MetaBase.xml file's location, always one level below the folder where the MetaBase.xml file is stored.

A history file pair consists of a MetaBase.xml and MBSchema.xml file of the same major and minor version numbers. The default setting allows for 10 versioned history file pairs to be stored in the history folder, but the number of file pairs stored in the history folder is configurable. However, before increasing the number of versioned sets of files stored in the history folder, you should ensure that you have adequate hard disk space on the drive volume where the history folder is located. (You can estimate the amount of hard disk space required by multiplying the average combined file size of MetaBase.xml and MBSchema.xml files by the number of versions that you want to store in the history folder.) You should not decrease the MaxHistoryFiles value below 10 if the Editing the MetaBase.XML File While IIS Is Running is enabled.

When the in-memory metabase is written to disk, IIS checks to determine whether the number of history file pairs contained in the history folder exceeds the value of the MaxHistoryFiles property. If the number of history file pairs exceed the MaxHistoryFiles value, the oldest history file pair, based on the timestamp value, is deleted.

Related Topics

- For information about configuring the metabase history feature, see Configuring the Metabase History Feature.
- For information about restoring the MetaBase.xml and/or MBSchema.xml files from history files, see Metabase Reliability.
- For more information about editing the MetaBase.xml file while IIS is running, see Editing the MetaBase.XML File While IIS Is Running.
- For information about the event log, search for `"event log"` in the Windows online help.

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