I/O is an acronym for Input/Output, which refers to the mechanism or process for the transfer of information between one system or component and another.

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which section of kernel, manages io requests?

I know that the Block IO layer in Linux io stack manages and schedules io requests. but i do not know where is this code? indeed, i wanna see the section of code in kernel which corresponds to this ...
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LVM Logical Volume (linear) best performance

As a system administrator, one thing I do very often is increase LV's size. In most cases I have to extend first the VG, adding a new disk (we are talking about virtual machines). I have got a lot of ...
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In which thread does block driver issue commands to block device?

I'm currently reading "Understanding The Linux Kernel" book, as I've understood block I/O request order is like this; user space call => vfs call => I/O scheduler call => block device driver call. ...
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388 views

iotop showing 1.5 MB/s of disk write, but all programs have 0.00 B/s

I don't understand iotop output: it shows ~1.5 MB/s of disk write (top right), but all programs have 0.00 B/s. Why? The video was taken as I was deleting the content of a folder with a few millions ...
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253 views

Why is OS constantly writing to disk (ext4) on a Ubuntu 14.04 machine? Is it normal?

I'm quite sure it didn't happen before I started using LUKS and LVM on my disk (2 or 3 weeks ago), but now root user is constantly (every 2-3 seconds) writing (not reading, just writing) on disk and I ...
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78 views

How to get the Serial Number of a disk by corresponding file in linux?

I know that for a disk in linux, we can use commands such as hdparm or smartctl to get its basic information. But for the implementation of these commands, I think all of them are implemented by ...
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53 views

Samba system calls for reading/writing files from/to NAS issued from Windows desktop client

Windows desktop machine is connected via 1GB Ehternet cable to personal NAS (under development) with Ubuntu on it. While reading and writing files (> 1GB size) from/to NAS strace was conducted to ...
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65 views

Linux huge IOPS difference - same disks

I've been investigating for some time regarding some IOPS issues I've been experiencing.. And my mind is getting crazy! I have two servers (one bought 2 weeks ago, another 1.5 years ago) that I ...
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41 views

Restoring in-memory/swapped page state on resume from hibernation

I'm a big fan of Linux's hibernation support, which works extremely well on all the (admittedly slightly older) hardware I've tried it on. I highly prefer it to full shutdown and power up. There's ...
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72 views

how does o_sync trigger pdflush?

When I write using o_sync, the write call returns once the data has been written to the disk. But how does o_sync force Linux to write the data to disk? Normally you would have to wait a maximum of ...
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28 views

SSD as write target during reads

I have a real-time application which always writes data to a RAID 10 HDD configuration in a sequential manner at around ~50 MB/s. It uses mmap and writing should never be blocked due to waiting I/O. ...
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258 views

Monitor a program's I/O

I have a program which spawns several child processes. I want to know which files this program and its children are creating, deleting, and modifying. inotifywait can tell me which files are being ...
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175 views

iowait monitoring in top on OSX/iMac

I'm trying to monitor the performance of a process on OSX 10 (iMac), specifically whether I/O is currently a bottleneck or not. I don't use the machine, hence I need something simple that the user can ...
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41 views

IO benchmark tools block size impact?

Many IO benchmark tools (fio, dd, etc...) provide way to set block size. Lets say that I change 4K to 64k and test read/write on mounted SATA disk. I will get higher data throughput in sequential ...
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188 views

Tuning Linux I/O Scheduler

I need a little help with properly tuning the Linux I/O Scheduler for spinning drives. I have a process that writes data to a huge (4-16TB) memory mapped file and is using SHED_FIFO. The kernel then ...
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2k views

What's the difference between ioremap and file operation mmap?

I'm currently working on a PCI device driver for Ubuntu. I have some example code about PCI driver, but I have difficult on understanding the ioremap and file_operation.mmap. The description of file ...
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188 views

mmap and slow DMA transfers

I have a process that reads data from a hardware device using DMA transfers at a speed of ~4 * 50MB/s and at the same time the data is processed, compressed and written to a 4TB memory mapped file. ...
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263 views

iotop and ionice -p show a different class/priority for the same process

After running ionice -c2 -n7 <PID> on an I/O-intensive process (VirtualBox VM) and checking the result with ionice -p <PID> it shows best-effort: prio 7 which is expected. But when ...
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125 views

How to prevent dd from freezing my system?

I want to fill the free space on my hard drive with a command like that : # dd if=/dev/zero of=z but it causes GNOME to freeze regularly for a few seconds. Even the mouse cursor is affected. How ...
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604 views

Accessing Memory Mapped I/O is slow

I have a Terasic-SoCKIT(fpga & arm cortex a9) and I have Linux running on the HPS. I'm trying to access the memory mapped I/O, wrote a simple character driver with functions "request_mem_region" ...
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352 views

How to find what is hammering my I/O?

On a Ubuntu Linux machine that is used as a webserver, I see that I'm really hammering the I/O: - dysphoria():~$ iostat -d 3 3 Linux 3.13.0-45-generic (dysphoria) 2015-10-20 _x86_64_ ...
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Disk benchmark IO depth clear out

When I'm manipulating over some benchmark tool I/O depth, what exactly am I changing? Let's say I have SATA disk on /dev/sda. If I run hdparm: root@linaro-gnome:~# hdparm -I /dev/sda | grep Queue ...
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195 views

How to force ssh-add to ask passphrase when loading RSA key from FIFO?

I've created the following RSA key (with passphrase): ssh-keygen -t rsa -f rsa_foo Now when adding the key in normal way, ssh-add asks for the passphrase fine: $ ssh-add rsa_foo Enter passphrase ...
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60 views

How would I monitor the running i/o statistics of an application?

In windows I find it incredibly useful to monitor total I/O read bytes to give myself an idea of how long a command line process is taking/will take to execute a task. For example, for capinfos: ...
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Bash passing input

I am using an open source tool to merge files with genomic ranges (Feature to similar to R language function 'merge'). The software can take only two input files at a time. Suppose if I have to merge ...
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78 views

where or how to see if data is still being transferred over usb to mass storage

The data transfer to my mp3 player is very slow via USB connection. I have a mp3-player from Samsung (YP-M1JCB/EDC) which I have connected to my Fedora linux (the pc connection in the mp3 player is ...
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88 views

How to know which programs support streaming I/O

As I understand it, programs that support streaming I/O can work with files more than the size of the memory. Is this correct? Is there a way to know which programs support streaming I/O?
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73 views

Why is IO so high when almost out of memory

On my work laptop with an SSD and no swap, I sometimes run out of memory when running RAM-expensive applications (virtual machine, etc). When that happens, the system becomes slow (expected) but what ...
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10k views

How to get total Read and write IOPS in linux

How do i get Read and write IOPS separately in Linux? using command line or in a programmatic way. i am installed sysstat package. Please tel me how do i calculate separately using sysstat package ...
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Can suspending lead to data loss on an external HDD?

Let's assume we have an external HDD using an ext4 filesystem, powered via USB. Some write is ordered on the external drive, not synced yet. Then the user wants to suspend the system. Provided no ...
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What's the philosophy behind delaying writing data to disk?

In Linux, a finished execution of a command such as cp or dd doesn't mean that the data has been written to the device. One has to, for example, call sync, or invoke the "Safely Remove" or "Eject" ...
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349 views

Disk I/O latency using /proc/vmstat file

How do I calculate disk read and write latency in Linux? Is it possible to do the calculation using /proc file system? I am using iostat and vmstat command. But I do not understand how the ...
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358 views

Linux Performance Measurements using /proc/vmstat

Am new to Linux, Please any one help. I want to calculate Input output performance using /proc/vmstat file? when i run command cat /proc/vmstat | grep pgpg The answer is pgpgin 726854 pgpgout ...
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2k views

CentOS 7 Live - Read-only file system error

I have loaded a CentOS 7 Gnome Live USB. I wanted to do some operations on it without touching the installed system on the computer, because I only want to try some things. I installed openssh-server ...
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60 views

What could cause dropping cache to be extremely slow on a large cluster?

I'm attempting to time file I/O on my disks. In order to make sure all the I/O is happening off the hard drives and not from ram, before I time any read, I run a drop cache command. Specifically, I ...
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How can I print current reads and writes to the filesystem on demand?

I am interested in getting statistics about filesystem reads and writes, specifically to an NFS mount. I know there are many tools such as iostat, nfsstat and inotifywait but there are issues I have ...
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338 views

NTFS partitions with high IO load causes consuming all processor time

My system (linux 3.16, ntfs-3g 2013.1.13AR.1) has 2 NTFS partitions and 2 ext4. I have 2 hard drives, each of them has 1 ntfs and 1 ext4. I've noticed that high inpit-ouput on NTFS partitions causes ...
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335 views

Performance of `tar -xf` (block size related)

I'm recently working on optimizing the performance of tar -xf, i.e. untar a file. I notice that under default settings, tar -xf calls writes to write 10 KiB output at a time in chunks. However, this ...
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48 views

Linux buffer(1) program — replacement? useful?

I used to heavily use the buffer(1) program especially in talking to tape drives. Its a program made in the 1990's to essentially use a circular shared memory buffer to speed up I/O between two piped ...
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2k views

High IO wait - How to determine the root cause?

I have a MySQL instance on two dedicated servers. One for the production, the other for the test platform. The 2 servers are pretty the same, the only difference is the RAID controller and the ...
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Find amount of IO occurring over various NFS mounts

When I run netstat | grep nfs, I get the currently mounted nfs connections for a given host in a cluster. If there is massive io happening over 1 (or 2) of the connections, how can I monitor this? Is ...
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2k views

High on %wa from top command, is there any way to constrain it?

Here's my last top info before it stucks: top - 18:26:10 up 238 days, 5:43, 3 users, load average: 1782.01, 1824.47, 1680.36 Tasks: 1938 total, 1 running, 1937 sleeping, 0 stopped, 0 zombie ...
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370 views

How can I tell which process is IO bound?

Suppose I have a large number of processes and one (or more) is IO bound, obvious by a high wa value in top. How can I pinpoint which process it is? Each process shows how much cpu is being used, but ...
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2k views

Know which process does I/O without iotop

On Linux, I want to know which process uses my disk I/O bandwith. I know I can use iotop but I have a machine where, for various reasons, iotop cannot be installed. How can I manually get that ...
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How do I check which files are written by an application?

On my system, sar reports an average write to disk about 5MB/s. Using dstat I found that it's not so permanently, but there are peaks to 30-50MB/s, and then are sleeps. Using iotop i found that most ...
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Inherit IO redirections from a script to another

When I redirect the output of a script within a script, I expect the redirection to be applied to the called script as well as the program called within it. A: ./B 2>> error.log B: ./...
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Linux Mint keyboard and mouse take a long time to work after boot

I turn my computer on, select my linux harddrive, and then I end up at the Linux mint encryption password area. I have to wait about 1 minute just for my keyboard and mouse to actually light up and ...
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458 views

Relationship between IO scheduler and cpu/process scheduler?

The concepts of IO scheduler and CPU scheduler confuse me. Below are my understanding: Linux uses CFS scheduler + nice values by default to schedule processes. Each process has an IO queue. There ...
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283 views

How to track down the source of I/O spikes?

I am using Linux as a desktop, and keep getting seemingly random I/O Spikes. The machine becomes unusably slow. At first I thought it was just that I don't have enough memory. But looking at the ...
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238 views

Set ionice for a multi-threaded application

I have a program that spawns multiple threads, all of which do fairly intensive IO, running on the background. I want to set the scheduling class to idle so that it doesn't clog up the system; however,...