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PHYBS(1)		FreeBSD	General	Commands Manual		      PHYBS(1)

     phybs -- reveal a storage device's	physical block size

     phybs [-rsw] [-l minsize] [-h maxsize] [-t	total] device

     The phybs utility runs a series of	I/O benchmarks designed	to reveal a
     storage device's physical block size by comparing the performance of
     small and large I/O operations at various (mis-)alignments.

     The phybs utility makes a series of passes	with increasing	block sizes.
     In	each pass, it either reads or writes (or both) a number	of non-consec-
     utive 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 device's 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 crite-
     ria will be significantly slower.

     The following options are available:

     -h	maxsize	 Specify the maximum block size	to test.  This must be a power
		 of two	and a multiple of the minimum block size (see -l).
		 The default is	eight times the	minimum	block size.

     -l	minsize	 Specify the minimum block size	to test.  This must be a power
		 of two	and a multiple of the device's logical block size.
		 The default is	the device's logical block size.

     -r		 Perform read operations.  This	is the default.

     -s		 Open the device in synchronous	mode.

     -t	total	 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 max-
		 imum block size (see -h).  For	best results, it should	also
		 be significantly larger than the device's on-board cache.
		 The default is	128 MB.

     -w		 Perform write operations.

     The phybs 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 in-
     terest about the actual device.

     The phybs utility reports the benchmark results, but makes	no attempt at
     interpreting them.

     The phybs utility returns EX_OK if	the benchmark completed	successfully,
     EX_USAGE if the parameters	specified on the command line were invalid,
     EX_PERM if	the user does not have permission to open the specified	de-
     vice, EX_IOERR if it was interrupted by an	I/O error, and EX_OSERR	if it
     was interrupted for any other reason.

     recoverdisk(1) sysexits(3)	diskinfo(8)

     The phybs utility and this	manual page were written by Dag-Erling
     Smorgrav <>.

FreeBSD	13.0		      September	26, 2011		  FreeBSD 13.0


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