Sponsored Content
Special Forums Hardware DD command using block device as input Post 302667079 by Corona688 on Thursday 5th of July 2012 03:05:43 PM
Old 07-05-2012
Quote:
Originally Posted by nytty
At the application level page size is an important concept, it's the unit of interaction with the disk.
Agreed.

However, you're not actually interacting with the raw disk in your tests. You're telling the OS to do so for you, which does as it pleases. It will turn a tiny read into a much larger read for you -- ruining your results.

Even the OS isn't dealing with the disk raw, here. The OS asks the disk and the disk does what it pleases, pulling things from its own cache -- ruining your results.

Not to mention, you're running huge programs to do tiny things, which drowns your numbers in meaningless noise -- ruining your results.

Too bad there's not a program that actually deals with disks the way you want already... Something which can tell you transfer rates, bus modes, and bus speeds. Something which can configure software and hardware read-ahead, flush hardware caches at will, and all that jazz, letting you compare results for different configurations. Something which you can actually tell 'read raw sector x', and it will do so.

They really ought to make a program like that.

I bet they'd call it hdparm.

Last edited by Corona688; 07-05-2012 at 04:21 PM..
 

10 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

what is the command for listing the device specs in solaris

Im looking to get the statistics on a machine memory, cpu speed drive size etc thanks in advance (3 Replies)
Discussion started by: simplimarvelous
3 Replies

2. Solaris

block device problem

Hi ...... I have file system problem when i try to mount get the following message : mount: /dev/rdsk/c1t4d0s7 not a block device .... I run fsck it's ok ,,,, after run newfs -N /dev/dsk/c1t4d0s7 and fsck -o b=535952 /dev/dsk/c1t4d0s7 .............it's ok ........ At the and when i try... (2 Replies)
Discussion started by: tt155
2 Replies

3. UNIX for Dummies Questions & Answers

problem with output of find command being input to basename command...

Hi, I am triying to make sure that there exists only one file with the pattern abc* in path /path/. This directory is having many huge files. If there is only one file then I have to take its complete name only to use furter in my script. I am planning to do like this: if ; then... (2 Replies)
Discussion started by: new_learner
2 Replies

4. Linux

shrinking root partition and using free space to create a block device

We are intending to protect a set of user specified files using LVM mirroring where the protected space on which the user files are stored is mirrored on an LV on a different disk. Our problem is that for a user with a custom layout has installed linux with 2 partitons for swap and / and there is... (0 Replies)
Discussion started by: kickdgrass
0 Replies

5. Red Hat

How to Block the USB device

Hi friends, I wanna know how to block USB devices in my RedHat flavor Operating system. regards, Prakash (3 Replies)
Discussion started by: prakashkumar41
3 Replies

6. Shell Programming and Scripting

Block device fs vs normal directory

I talked with this guy who seems to think loop mounting a fs ext3 image on a directory, as opposed to just using the underlying filesystem, will work better as far as IO conflicts. I have no idea why this would be better? I haven't been able to contact him. Basically we have a daemon that... (0 Replies)
Discussion started by: stevenswj
0 Replies

7. Linux

Block device fs vs normal directory

I use CentOS I talked with this guy who seems to think loop mounting a fs ext3 image on a directory, as opposed to just using the underlying filesystem, will work better as far as IO conflicts. I have no idea why this would be better? I haven't been able to contact him. Basically we have a... (1 Reply)
Discussion started by: stevenswj
1 Replies

8. Shell Programming and Scripting

tcgetattr: Inappropriate ioctl for device after ssh command

Hello everyone I am finishing a script allowing me to purge logs on multiple servers, i have one last pb with the ssh command.........it is throwing me the following error : tcgetattr: Inappropriate ioctl for device (full screen in attached file 1, full script in attached file 2) It... (15 Replies)
Discussion started by: jimmy75_13
15 Replies

9. UNIX for Advanced & Expert Users

Command to see the logical volume path, device mapper path and its corresponding dm device path

Currently I am using this laborious command lvdisplay | awk '/LV Path/ {p=$3} /LV Name/ {n=$3} /VG Name/ {v=$3} /Block device/ {d=$3; sub(".*:", "/dev/dm-", d); printf "%s\t%s\t%s\n", p, "/dev/mapper/"v"-"n, d}' Would like to know if there is any shorter method to get this mapping of... (2 Replies)
Discussion started by: royalibrahim
2 Replies

10. OS X (Apple)

Change Name of Bluetooth Device from Command Line in macOS

Mac Version 10.15.2 (macOS Catalina) Does anyone know how to change the name of a connected bluetooth device from the command line on macOS? I am having trouble with various bluetooth devices which I cannot get the "rename" option in the GUI to "save" properly and so I cannot rename a few... (0 Replies)
Discussion started by: Neo
0 Replies
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)
All times are GMT -4. The time now is 10:00 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy