Provided by: sg-utils_1.02-1_i386
sg_read - read blocks of data continually from same offset
Read data from a Linux SCSI generic (sg) device, a raw devices or a
normal file with each read command issued to the same offset. This will
test (or time) disk caching and/or SCSI (or some other) bus throughput.
each read operation will be made using this number of blocks (or
less if near the end of count). Default is 128. Note also that
each read operation starts at the same offset (as given by skip
this must be the block size of the physical device (defaults to
read this number of blocks. This argument must be given
read from this FILE. This argument must be given
all read operations will start offset by BLOCKS bs-sized blocks
from the start of input (file or device)
time=0 | 1 | 2
When 0 (default) doesn’t perform timing. when 1, times transfer
and does throughput calculation, starting at the first issued
command until completion. When 2, times transfer and does
throughput calculation, starting at the second issued command
The input file must be either a sg device, a raw device or a normal
file. A raw device must be bound to a block device prior to using
sg_raw. See raw(8) for more information about binding raw devices.
BYTES and BLOCKS may be followed by the following multiplicative
suffixes: c C *1; b B *512; k *1,024; K *1,000; m *1,048,576; M
*1,000,000; g *1,073,741,824; and G *1,000,000,000
Let us assume that /dev/sg0 is a disk and we wish to time the disk’s
sg_read if=/dev/sg0 bs=512 count=1M time=2
This command will continually read 128 512 byte blocks from block 0.
The "128" is the default value for "bpt" while "block 0" is chosen
because the "skip" argument was not given. This will continue until
1,000,000 blocks are read. The idea behind using "time=2" is that the
first 64 KB read operation will involve reading the magnetic media
while the remaining read operations will "hit" the disk’s cache. The
output of thid command will look like this:
time from second command to end was 8.51 secs, 60.19 MB/sec
1000000+0 records in, SCSI commands issued: 7813
Written by Doug Gilbert.
Report bugs to <firstname.lastname@example.org>.
Copyright © 2000-2002 Douglas Gilbert
This software is distributed under the GPL version 2. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
To time streaming media read or write time see sg_dd is in the sg_utils
package. The lmbench package contains lmdd which is also interesting.