JFS Tuning and Performance

Creating your file system

When you create a file system using newfs(1m) or mkfs(1m), you need to be aware of several options

that could affect performance.

Block size

The block size (bsize) is the smallest amount of space that can be allocated to a file extent. Most

applications will perform better with an 8 KB block size. Extent allocations are easier and file systems

with an 8 KB block size are less likely to be impacted by fragmentation since each extent would have

a minimum size of 8 KB. However, using an 8 KB block size could waste space, as a file with 1 byte

of data would take up 8 KB of disk space.

The default block size for a file system scales depending on the size of the file system when the file

system is created. The fstyp(1M) command can be used verify the block size of a specific file system

using the f_frsize field. The f_bsize can be ignored for VxFS file systems as the value will always be

8192.

# fstyp -v /dev/vg00/lvol3

vxfs

version: 6

f_bsize: 8192

f_frsize: 8192

The following table documents the default block sizes for the various VxFS versions beginning with

VxFS 3.5 on 11.23:

Table 2. Default FS block sizes

FS Size

DLV 4

DLV 5

>= DLV6

<2TB

<4TB

N/A

<8TB

N/A

<16TB

N/A

<32TB

N/A

>= 32TB

N/A

For most cases, the block size is not important as far as reading and writing data is concerned (with

the exceptions regarding direct I/O alignment discussed earlier). The block size is an allocation

policy parameter, not a data access parameter.

Intent log size

The default size of the intent log (logsize) scales depending on the size of the file system. The logsize

is specified as the number of file system blocks. The table below provides details on the default size of

the Intent Log in megabytes (MB).

VxFS disk version layout 5 (11.23) and HP OnlineJFS license is needed to create file systems past 2TB.

The EBFS license is needed to create file systems past 32TB.