Configure Network Services - MCSA Windows Server 2012 R2: Installation and Configuration Study Guide - page 155

open when the DHCP service is running. DHCP servers use Joint Engine Technology (JET)
databases to maintain their records.

You shouldn't modify or alter the DHCP database files when the service is
running.

The primary database file is dhcp.mdb —it has all of the scope data in it.
The following files are also part of the DHCP database:
Dhcp . tmp This is a backup copy of the database file created during reindexing of the
database. You normally won't see this file, but if the service fails during reindexing, it may
not remove the file when it should.
J50 . log This file (plus a number of files named J50xxxxx . log , where xxxxx stands for
00001, 00002, 00003, and so on) is a log file that stores changes before they're written to
the database. The DHCP database engine can recover some changes from these files when it
restarts.
J50 . chk This is a checkpoint file that tells the DHCP engine which log files it still needs to
recover.

In the following sections, you will see how to manipulate the DHCP database files.

Removing the Database Files
If you're convinced that your database is corrupt because the lease information that you
see doesn't match what's on the network, the easiest repair mechanism is to remove the
database files and start over with an empty database.

If you think the database is corrupt because the DHCP service fails at
startup, you should check the event log.

To start over, follow these steps:

1.

Stop the DHCP service by typing net stop dhcpserver at the command prompt.

2.

Remove all of the files from the systemroot\system32\DHCP folder.

3.

Restart the service (at command prompt type net start dhcpserver ).

4.

Reconcile the scope.

Changing the Database Backup Interval
By default, the DHCP service backs up its databases every 60 minutes. You can adjust
this setting by editing the Backup Interval value under HKEY_LOCAL_MACHINE\SYSTEM\
CurrentControlSet\Services\DHCPServer\Parameters . This allows you to make backups
either more frequently (if your database changes a lot or if you seem to have ongoing
corruption problems) or less often (if everything seems to be on an even keel).