Veritas™ File System 5.0.1 Administrator's Guide

The blkclear mode

The blkclear mode is used in increased data security environments. The blkclear

mode guarantees that uninitialized storage never appears in files. The increased

integrity is provided by clearing extents on disk when they are allocated within

a file. This mode does not affect extending writes. A blkclear mode file system

is approximately 10 percent slower than a standard mode VxFS file system,

depending on the workload.

The mincache mode

The mincache mode has the following suboptions:

■ mincache=closesync

■ mincache=direct

■ mincache=dsync

■ mincache=unbuffered

■ mincache=tmpcache

The mincache=closesync mode is useful in desktop environments where users

are likely to shut off the power on the machine without halting it first. In this

mode, any changes to the file are flushed to disk when the file is closed.

To improve performance, most file systems do not synchronously update data

and inode changes to disk. If the system crashes, files that have been updated

within the past minute are in danger of losing data. With the mincache=closesync

mode, if the system crashes or is switched off, only open files can lose data. A

mincache=closesync mode file system could be approximately 15 percent slower

than a standard mode VxFS file system, depending on the workload.

The following describes where to use the mincache modes:

■ The mincache=direct, mincache=unbuffered, and mincache=dsync modes

are used in environments where applications have reliability problems caused

by the kernel buffering of I/O and delayed flushing of non-synchronous I/O.

■ The mincache=direct and mincache=unbuffered modes guarantee that all

non-synchronous I/O requests to files are handled as if the VX_DIRECT or

VX_UNBUFFERED caching advisories had been specified.

■ The mincache=dsync mode guarantees that all non-synchronous I/O requests

to files are handled as if the VX_DSYNC caching advisory had been specified.

Refer to the vxfsio(7) manual page for explanations of VX_DIRECT,

VX_UNBUFFERED, and VX_DSYNC, as well as for the requirements for direct I/O.

VxFS performance: creating, mounting, and tuning file systems

Mounting a VxFS file system