There are several characteristics that you can select when
you create a file system. The most important options pertaining
to system performance are the block size and intent log size.
Block Size |
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The unit of allocation in VxFS is a block. Unlike some other
UNIX file systems, VxFS does not make use of block fragments for
allocation because storage is allocated in extents that consist
of one or more blocks.
You specify the block size when creating a file system by
using the mkfs -o bsize option. The block size cannot be altered after the file
system is created. The smallest available block size for VxFS is
1K. The minimum block size must be 2K for file systems from 4 TB
to 8 TB, 4K for file systems from 8 TB to 16 TB, and 8K for file
systems larger than 16 TB (see “The
VxFS Version 5 Disk Layout”“ for more information).
Choose a block size based on the type of application being
run. For example, if there are many small files, a 1K block size
may save space. For large file systems, with relatively few files,
a larger block size is more appropriate. Larger block sizes use
less disk space in file system overhead, but consume more space
for files that are not a multiple of the block size. The easiest
way to judge which block sizes provide the greatest system efficiency
is to try representative system loads against various sizes and
pick the fastest.
Intent Log Size |
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You specify the intent log size when creating a file system
by using the mkfs -o logsize option. The intent log size cannot be altered after the
file system is created. The mkfs utility uses a default intent log size of 256K for file
systems less than 8 megabytes, 1024K for file systems from 8 to
512 megabytes, and 16 megabytes for file systems greater than 512
megabytes. The default size is sufficient for most workloads. If the
system is used as an NFS server or for intensive synchronous write
workloads, performance may be improved using a larger log size.
With larger intent log sizes, recovery time is proportionately
longer and the file system may consume more system resources (such
as memory) during normal operation.
There are several system performance benchmark suites for
which VxFS performs better with larger log sizes. As with block
sizes, the best way to pick the log size is to try representative
system loads against various sizes and pick the fastest.
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