VERITAS File System 3.5 (HP OnlineJFS/JFS 3.5) Administrator's Guide (August 2003)

Chapter 2
VxFS Performance: Creating, Mounting, and Tuning File Systems
Choosing mount Command Options
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nodatainlog
Use the nodatainlog mode on systems with disks that do not support bad block revectoring. Usually, a VxFS
file system uses the intent log for synchronous writes. The inode update and the data are both logged in the
transaction, so a synchronous write only requires one disk write instead of two. When the synchronous write
returns to the application, the file system has told the application that the data is already written. If a disk
error causes the metadata update to fail, then the file must be marked bad and the entire file is lost.
If a disk supports bad block revectoring, then a failure on the data update is unlikely, so logging synchronous
writes should be allowed. If the disk does not support bad block revectoring, then a failure is more likely, so
the nodatainlog mode should be used.
A nodatainlog mode file system is approximately 50 percent slower than a standard mode VxFS file system
for synchronous writes. Other operations are not affected.
blkclear
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. Extending writes are not affected by this mode. A blkclear mode file
system is approximately 10 percent slower than a standard mode VxFS file system, depending on the
workload.
mincache
The mincache mode has five 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 files that are currently open can lose
data. A mincache=closesync mode file system should be approximately 15 percent slower than a standard
mode VxFS file system, depending on the workload.
The mincache=direct, mincache=unbuffered, and mincache=dsync modes are used in environments where
applications are experiencing 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 will be 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 will be 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. The mincache=direct,
mincache=unbuffered, and mincache=dsync modes also flush file data on close as mincache=closesync
does.