Manual Reference Pages - PHYBS (1)
- reveal a storage devices physical block size
utility runs a series of I/O benchmarks designed to reveal a storage
devices physical block size by comparing the performance of small and
large I/O operations at various (mis-)alignments.
utility makes a series of passes with increasing block sizes.
In each pass, it either reads or writes (or both) a number of
non-consecutive blocks at increasing offsets relative to the ideal
alignment, which is assumed to be multiples of the block size.
The results are presented in terms of time elapsed, transactions per
second and kB per second.
If the devices physical block size is larger than its logical block
size, peak performance will be obtained when reading or writing
multiples of the physical block size at offsets which are also
multiples of the physical block size, while I/O operations which do
not meet these criteria will be significantly slower.
The following options are available:
Specify the maximum block size to test.
This must be a power of two and a multiple of the minimum block size
The default is eight times the minimum block size.
Specify the minimum block size to test.
This must be a power of two and a multiple of the devices logical
The default is the devices logical block size.
Perform read operations.
This is the default.
Open the device in synchronous mode.
Specify the total amount of data to read or write in each pass.
This must be a power of two and a multiple of the maximum block size
For best results, it should also be significantly larger than the
devices on-board cache.
The default is 128 MB.
Perform write operations.
utility can be used on files as well as raw devices, but the
characteristics of the underlying file system will greatly influence
the results, possibly to the point where they can not reveal anything
of interest about the actual device.
utility reports the benchmark results, but makes no attempt at
if the benchmark completed successfully,
if the parameters specified on the command line were invalid,
if the user does not have permission to open the specified device,
if it was interrupted by an I/O error, and
if it was interrupted for any other reason.
utility and this manual page were written by
.An Dag-Erling Smrgrav Aq des@FreeBSD.org .
Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.