sg_test_rwbuf(8) [suse man page]
SG_TEST_RWBUF(8) SG3_UTILS SG_TEST_RWBUF(8) NAME
sg_test_rwbuf - Tests the SCSI host adapter by issuing write and read operations on a device's buffer and calculating checksums. SYNOPSIS
sg_test_rwbuf [--addrd=AR] [--addwr=AW] [--help] [--quick] --size=SZ [--times=NUM] [--verbose] [--version] DEVICE or an older deprecated format sg_test_rwbuf DEVICE SZ [AW] [AR] DESCRIPTION
sg_test_rwbuf writes and reads back SZ bytes to the internal buffer of DEVICE (e.g. /dev/sda or /dev/sg0). A pseudo random pattern is writ- ten to the data buffer on the device then read back. If the same pattern is found 'Success' is reported. If they do not match (checksums unequal) then this is reported and up to 24 bytes from the first point of mismatch are reported; the first line shows what was written and the second line shows what was received. For testing purposes, you can ask it to write AW or read AR additional bytes. OPTIONS
Arguments to long options are mandatory for short options as well. -r, --addrd=AR Read an additional AR bytes (than indicated by SZ) from the data buffer. Checksum is performed over the first SZ bytes. -w, --addwr=AW Write an additional AW bytes (than indicated by SZ) of zeros into the data buffer. Checksum is generated over the first SZ bytes. -h, --help Print out a usage message the exit. -q, --quick Perform a READ BUFFER descriptor command to find out the available data buffer length and offset, print them out then exit (without testing with write/read sequences). -s, --size=SZ where SZis teh size of buffer in bytes to be written then read and checked. This number needs to be less than on equal to the size of the device's data buffer which can be seen from the --quick option. Either this option or the --quick option should be given. -t, --times=NUM where NUM is the number of times to repeat the write/read to buffer test. Default value is 1 . -v, --verbose increase verbosity of output. -V, --version print version number (and data of last change) then exit. NOTES
The microcode in a SCSI device is _not_ modified by doing a WRITE BUFFER command with its mode set to "data" (0x2) as done by this utility. Therefore this utility is safe in that respect. [Mode values 0x4, 0x5, 0x6 and 0x7 are the dangerous ones :-)] WARNING: If you access the device at the same time (e.g. because it's a hard disk with a mounted file system on it) the device's buffer may be used by the device itself for other data at the same time, and overwriting it may or may not cause data corruption! HOWEVER the SPC-3 draft standard does state in its WRITE BUFFER command: "This command shall not alter any medium of the logical unit when data mode ... is specified". This implies that it _is_ safe to use this utility with devices that have mounted file systems on them. Following this theme further, a disk with active mounted file systems may cause the data read back to be different (due to caching activity) to what was written and hence a checksum error. EXIT STATUS
The exit status of sg_test_rwbuf is 0 when it is successful. Otherwise see the sg3_utils(8) man page. AUTHORS
Written by D. Gilbert and K. Garloff COPYRIGHT
Copyright (C) 2000-2006 Douglas Gilbert, Kurt Garloff This software is distributed under the GPL version 2. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR- POSE. sg3_utils-1.23 January 2007 SG_TEST_RWBUF(8)
Check Out this Related Man Page
SG_RBUF(8) SG3_UTILS SG_RBUF(8) NAME
sg_rbuf - reads data using SCSI READ BUFFER command SYNOPSIS
sg_rbuf [--buffer=EACH] [--dio] [--help] [--mmap] [--quick] [--size=OVERALL] [--test] [--verbose] [--version] DEVICE sg_rbuf [-b=EACH_KIB] [-d] [-m] [-q] [-s=OVERALL_MIB] [-t] [-v] [-V] DEVICE DESCRIPTION
This command reads data with the SCSI READ BUFFER command and then discards it. Typically the data being read is from a disk's memory cache. It is assumed that the data is sourced quickly (although this is not guaranteed by the SCSI standards) so that it is faster than reading data from the media. This command is designed for timing transfer speeds across a SCSI transport. To fetch the data with a SCSI READ BUFFER command and optionally decode it see the sg_read_buffer utility. There is also a sg_write_buffer utility useful for downloading firmware amongst other things. This utility supports two command line syntaxes, the preferred one is shown first in the synopsis and explained in this section. A later section on the old command line syntax outlines the second group of options. OPTIONS
Arguments to long options are mandatory for short options as well. -b, --buffer=EACH where EACH is the number of bytes to be transferred by each READ BUFFER command. The default is the actual available buffer size returned by the READ BUFFER (descriptor) command. The maximum is the same as the default, hence this argument can only be used to reduce the size of each transfer to less than the device's actual available buffer size. -d, --dio use direct IO if available. This option is only available if the DEVICE is a sg driver device node (e.g. /dev/sg1). In this case the sg driver will attempt to configure the DMA from the SCSI adapter to transfer directly into user memory. This will eliminate the copy via kernel buffers. If not available then this will be reported and indirect IO will be done instead. -h, --help print usage message then exit. -m, --mmap use memory mapped IO if available. This option is only available if the DEVICE is a sg driver device node (e.g. /dev/sg1). In this case the sg driver will attempt to configure the DMA from the SCSI adapter to transfer directly into user memory. This will elimi- nate the copy via kernel buffers. -O, --old switch to older style options. -q, --quick only transfer the data into kernel buffers (typically by DMA from the SCSI adapter card) and do not move it into the user space. This option is only available if the DEVICE is a sg driver device node (e.g. /dev/sg1). -s, --size=OVERALL where OVERALL is the size of total transfer in bytes. The default is 200 MiB (200*1024*1024 bytes). The actual number of bytes transferred may be slightly less than requested since all transfers are the same size (and an integer division is involved rounding towards zero). -t, --time times the bulk data transfer component of this command. The elapsed time is printed out plus a MB/sec calculation. In this case "MB" is 1,000,000 bytes. The gettimeofday() system call is used internally for the time calculation. -v, --verbose increase level of verbosity. Can be used multiple times. -V, --version print out version string then exit. NOTES
This command is typically used on modern SCSI disks which have a RAM cache in their drive electronics. If no IO to the magnetic media, or slower devices like flash RAM, is involved then the disk may be able to source data fast enough to saturate the bandwidth of the SCSI transport. The bottleneck may then be the DMA element in the HBA, the Linux drivers or the host machine's hardware (e.g. speed of RAM). Various numeric arguments (e.g. OVERALL) may include multiplicative suffixes or be given in hexadecimal. See the "NUMERIC ARGUMENTS" sec- tion in the sg3_utils(8) man page. EXAMPLES
On the test system /dev/sg0 corresponds to a fast disk on a U2W SCSI bus (max 80 MB/sec). The disk specifications state that its cache is 4 MB. $ time ./sg_rbuf /dev/sg0 READ BUFFER reports: buffer capacity=3434944, offset boundary=6 Read 200 MiB (actual 199 MiB, 209531584 bytes), buffer size=3354 KiB real 0m5.072s, user 0m0.000s, sys 0m2.280s So that is approximately 40 MB/sec at 40 % utilization. Now with the addition of the "-q" option this throughput improves and the utiliza- tion drops to 0%. $ time ./sg_rbuf -q /dev/sg0 READ BUFFER reports: buffer capacity=3434944, offset boundary=6 Read 200 MiB (actual 199 MiB, 209531584 bytes), buffer size=3354 KiB real 0m2.784s, user 0m0.000s, sys 0m0.000s EXIT STATUS
The exit status of sg_rbuf is 0 when it is successful. Otherwise see the sg3_utils(8) man page. OLDER COMMAND LINE OPTIONS
The options in this section were the only ones available prior to sg3_utils version 1.23 . In sg3_utils version 1.23 and later these older options can be selected by either setting the SG3_UTILS_OLD_OPTS environment variable or using '--old' (or '-O) as the first option. -b=EACH_KIB where EACH_KIB is the number of Kilobytes (i.e. 1024 byte units) to be transferred by each READ BUFFER command. Similar to the --buffer=EACH option in the main description but the units are different. -d use direct IO if available. Equivalent to the --dio option in the main description. -m use memory mapped IO if available. Equivalent to the --mmap option in the main description. -N switch to the newer style options. -q only transfer the data into kernel buffers (typically by DMA from the SCSI adapter card) and do not move it into the user space. Equivalent to the --quick option in the main description. -s=OVERALL_MIB where OVERALL_MIB is the size of total transfer in Megabytes (1048576 bytes). Similar to the --size=OVERALL option in the main description but the units are different. -t times the bulk data transfer component of this command. Equivalent to the --time option in the main description. -v increase level of verbosity. Can be used multiple times. -V print out version string then exit. AUTHOR
Written by Douglas Gilbert REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>. COPYRIGHT
Copyright (C) 2000-2007 Douglas Gilbert This software is distributed under the GPL version 2. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR- POSE. SEE ALSO
sg_read_buffer, sg_write_buffer, sg_test_rwbuf(all in sg3_utils) sg3_utils-1.23 January 2007 SG_RBUF(8)