Service manual

Sizing Disk Subsystems
Chapter 4 Hardware Sizing 87
Transaction Log
Transaction log volume depends upon peak write loads. If writes occur in bursts,
transaction logs use more space than if the write load is constant. Directory Server
trims transaction logs periodically. Transaction logs therefore should not continue
to grow unchecked. Transaction logs are not, however, flushed during online
backup.
Directory Server is generally run with durable transactions enabled. When durable
transaction capabilities are enabled, Directory Server performs a synchronous
write to the transaction log for each modification (
add, delete, modify, modrdn)
operation. In this case, an operation can beblocked if the disk is busy, resulting in a
potential I/O bottleneck.
If update performance is critical, plan to use a disk subsystem having fast write
cache for the transaction log. Refer to Chapter 8, “Tuning Logging,” for further
information.
Replication Changelog Database
If the deployment involves replication, the Directory Server suppliers perform
change logging. Changelog size depends on the volume of modifications and on
the type of changelog trimming employed. Plan capacity based on how the
changelog is trimmed. For a large, high load deployment, consider setting aside
several gigabytes of disk space to handle changelog growth during periods of
abnormallyhigh modification rates.Refer to Chapter 8, “Tuning Logging,” for
further information.
Suffix Initialization and LDIF Files
During suffix initialization, also called bulk loading or importing, the Directory
Server requires disk space not only for the suffix database files and the LDIF used
to initialize the suffix, but also for intermediate files used during the initialization
process. Plan extra (temporary) capacity in the same directory as the database files
for the LDIF files and for the intermediate files used during suffix initialization.
Backups and LDIF Files
Backups often consume a great deal of disk space. The size ofa backup equals the
size of the database files involved. Accommodate for several backups by allocating
space equal to several times the volume of the database files, ensuring that
databases and their corresponding backups are maintained on separate disks.
Employ intelligent strategies for migrating backups to cheaper storage mediums as
they age.