Sponsored Content
Special Forums Hardware DD command using block device as input Post 302666061 by Corona688 on Tuesday 3rd of July 2012 03:43:10 PM
Old 07-03-2012
Quote:
Originally Posted by nytty
Alright, I get your point. I though that using /dev/sdb1 moves to position 0 Smilie
AFAIK hdparm only gives you the speed of the disk and not the time of reading a given amount of data.
Do a little math. x megabytes per second is 1/x seconds per megabyte.

Quote:
So far with my tests I find that reading 16kb takes about the same time as reading 512b.
Disks do read-ahead for you. Disks transfer to the host in larger bundles than 512 bytes anyway. Disks even do their own caching which the OS has no control over, which is going to throw off all your results supremely.

Too bad there isn't a tool which can tell you more about what your disk's doing, test uncached reads, or even configure hardware read-ahead to your preference... something like hdparm...
Quote:
I need this information to set the optimal page size of my system (oracle and mysql suggest these sizes)
Tell me exactly what they're asking you. I suspect you've gotten it a bit mixed up.
Quote:
Can you elaborate on why dropping the caches is a bad idea?
Because it's not realistic. Your system needs cache to work. Disk speeds are going to be awful without it.
Quote:
How about this sudo procedure:
- drop_caches
- flush disk-cache with hdparm
- make sure dd is in memory
- position the read head randomly on disk
- with DD: read X amount of bytes from the beginning of my file (this is timed)
Same problem as the exact same thing you did before. YOu're running huge programs to do tiny things and your results are going to be meaningless.

Last edited by Corona688; 07-03-2012 at 04:51 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
SMFPLAY(1)						    BSD General Commands Manual 						SMFPLAY(1)

NAME
smfplay -- play a standard MIDI file SYNOPSIS
smfplay [-mxy] [-g measure] [-d devname] [-i devname] midifile DESCRIPTION
The smfplay utility plays a MIDI file. While playing, it can route events from one midi(4) device to another. To stop performance, send an interrupt signal to smfplay (for instance by pressing control ^C on the terminal). The options are as follows: -m Use metronome. The metronome will follow tempo changes and time signature changes in the midi file. -x Synchronise to an external midi(4) device. If the -i flag is used then playback will be synchronised to the input device else it will be synchronised to the default device. -y Send midi timing information to the default device. Useful if the output device is a slave MIDI sequencer. -g measure Start playback at the given measure number. -d filename Default midi(4) device on which to play the midi file. If not specified, the content of the MIDIDEV environment variable will be used instead. -i filename Alternate input midi(4) device. Voice events (notes, controllers, etc) received on the input device will be sent as-is to the default device. Without this flag, the default device will be used for input. The smfplay utility is an interface to midish(1). If more specific features are needed, the user may consider using midish(1). EXAMPLES
The following will play mysong.mid on device /dev/rmidi4 and will use metronome. $ smfplay -m -d /dev/rmidi4 mysong.mid SEE ALSO
smfrec(1), midish(1), midiplay(1), midi(4) BSD
August 22, 2005 BSD
All times are GMT -4. The time now is 08:26 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy