VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 9

VERITAS QuickLog

VERITAS QuickLog Overview

The VxFS intent log is stored near the beginning of the volume on which the file system resides (The word

volume here describes either a VERITAS Volume Manager (VxVM) volume or a raw disk partition). VxFS log

writes are sequential, meaning that each log record is written to disk where the previous log record finished.

The performance of the log writes is limited because the file system is doing other operations (inode updates,

reading and writing data) that require reads and writes from other areas of the disk. The disk head is

constantly seeking between the log and data areas of VxFS, reducing the benefits associated with sequential

writes to disk.

QuickLog improves file system performance by eliminating the time that a disk spends seeking between the

log and data areas of VxFS. This is accomplished by exporting the file system intent log to a separate physical

volume called a QuickLog device. A QuickLog device should not reside on a physical disk that shares space

with other file systems, since the performance improvement that QuickLog provides depends on the disk head

always being in position to write the next log record.

QuickLog is transparent to the end user and requires a minimum of intervention or training to operate.

NOTE QuickLog cannot be enabled on a root file system.

The figure on the following page shows a logical view of QuickLog and how it interfaces with the operating

system.

QuickLog Setup

VERITAS QuickLog supports:

• Up to 63 QuickLog devices

— Up to 31 local QuickLog devices

— Up to 32 cluster QuickLog devices

• Up to 32 VxFS file systems per QuickLog device

• From one to four QuickLog volumes per QuickLog device (see “QuickLog Load Balancing” on page 92 for

details)

• Communication between QuickLog and VxFS through an integrated interface