Service manual

Sizing Disk Subsystems
Chapter 4 Hardware Sizing 89
Transaction Logs
When durable transaction capabilities are enabled, Directory Server performs a
synchronous write to the transaction log for each modification operation. An
operation is thus blocked when the disk is busy. Placing transaction logs on a
dedicated disk can improve write performance, and increase the modification rate
Directory Server can handle.
Refer to “Transaction Logging,” on page 147 for more information.
Databases
Multiple database support allows each database to reside on its own physical disk.
You can thus distribute the Directory Server load across multiple databases each
on its own disk subsystem. To prevent I/O contention for database operations,
consider placing each set of database files on a separate disk subsystem.
Fortop performance,place databasefilesonadedicatedfast disk subsystemwith a
large I/O buffer. Directory Server reads data from the disk when it cannot find
candidate entries in cache. It regularly flushes writes. Having a fast, dedicated disk
subsystem for these operations can alleviate a potential I/O bottleneck.
The
nsslapd-directory attribute on cn=config,cn=ldbm
database,cn=plugins,cn=config
specifies the disk location where Directory
Server stores database files, including index files. By default, such files are located
under
ServerRoot/slapd-ServerID/db/.
Changing database locationof course requires not only that you restart Directory
Server, but also that you rebuild the database completely. Changing database
location on a production server can be a major undertaking, so identify your most
important database and put it on a separate disk before putting the server into
production.
Log Files
Directory Server provides access, error, and audit logs featuring buffered logging
capabilities. Despite buffering, writes to these log files require disk access that may
contend with other I/O operations. Consider placing log files on separate disks for
improved performance, capacity, and management.
Refer to Chapter 8, “Tuning Logging,” for more information.