Difference between buffered disk reads and cached reads? Post: 302538491

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LEARN ABOUT DEBIAN

sraw

SRAW(8) 						      System Manager's Manual							   SRAW(8)

NAME

       sraw - benchmark raw scsi I/O performance under linux

SYNOPSIS

       sraw [ -fiv6 ] scsi-device [ bstart [ bstep ] ]

DESCRIPTION

       This  program  basically  reads the specified scsi device and measures the throughput.  Note that the filesystem *AND* the buffer cache are
       bypassed by this code, this program was designed to benchmark the naked scsi drivers by themselves without the  need  to  account  for  the
       overhead of any other portion of the kernel. It also could be used to benchmark disk read throughput.

       This  program  does  a  series of reads of the disk, of consecutive areas on the disk.  The device is first queried to determine the sector
       size for the device, and then the series of reads is begun.  About 5.0 Mb is read from the device, and then  the  performance  numbers  are
       reported.  Note that since the buffer cache is completely bypassed, there is no need to be concerned about cache hits or anything.

       Output of sraw is a set of lines, 4 numbers per line: blocksize, elapsed time, nblocks and throughput (in bytes per second).

       scsi-device is either a block device (e.g. /dev/sda, /dev/scd0) or a generic SCSI device (e.g. /dev/sg0).

OPTIONS

       -f     set FUA (Force Unit Access) bit during read. Data is then read from media instead of internal drive cache.

       -i     use legacy ioctl instead of new SG I/O layer (will not work on 2.6 kernel and block devices).

       -v     more verbose output.

       -6     use 6-bytes instead of 10-bytes read command. In this case, only the first GB of data could be read from media.

       bstart starting block to check different zones on ZBR discs

       bstep  factor for sequential stepping, default 1.  Use 0 for reading always the same blocks (from cache)

ERRORS

       sraw  could  issue input/output errors when reading too many blocks at the same time from a block device like /dev/sda. To get rid of them,
       use /dev/sgN instead.

AUTHOR

       sraw was first written by Eric Youngdale.  Extensions (-v, -f, -6, SG IO, man page) were written by Eric Delaunay.

SEE ALSO

       sg_dd(8) from sg3-utils package.

AVAILABILITY

       sraw is available at
       ftp://tsx-11.mit.edu/pub/linux/ALPHA/scsi/

								     Nov 1993								   SRAW(8)