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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18
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When is dd suitable for copying data? (or, when are read() and write() partial)

Short version: In what circumstances is dd safe to use for copying data, safe meaning that there is no risk of corruption due to a partial read or write? Long version — preamble: dd is often used to ...
11
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2answers
1k views

Weight-based block IO control for VMs

I use KVM to manage my virtual machines. I am trying to limit the resources provided for VMs. I am able to limit the CPU and memory allocated for VMs using libvirt/cgroups. Now I want to control the ...
7
votes
3answers
8k views

Find out what processes are writing to hard drive

On my Lenovo T400 and Ubuntu, the light for hard drive writing keeps flashing. I was wondering if in Linux it is possible to find out what processes are doing I/O to the hard drive? Just like by top, ...
1
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1answer
250 views

performance on Linux system when daisy-chaining multiple USB hard-drives on USB hubs?

What would the I/O access be like as I plug many USB drives into a Linux system with only 2 USB 2.0 ports and 1 USB 3.0 port? I expect I will have to have multiple levels of fan-out by plugging hubs ...
0
votes
1answer
133 views

What Linux tool will tell me if all the mounted disks share roughly the same bandwidth?

What Linux tool will tell me if all the mounted disks share roughly the same bandwidth? Can I do something like iostat for each of my /dev/sd* devices?
2
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1answer
295 views

Pluggin a bunch of USB hard drives into a Linux system?

I've got a Linux system with two USB 2.0 ports and one USB 3.0 port, and I would like to know how many USB hard drives I could plug into it. On the performance side, what would the I/O access be like ...
0
votes
1answer
268 views

How to test the difference between using disk encryption or not?

If I have a laptop, and I want to install an Ubuntu 11.04 on it, but disk performance would be an important thing, then how could I test the real differences between: - not using encryption - ...
4
votes
3answers
1k views

Intercept input and output from specific executable

I have a certain Linux executable that is called from a bigger application to perform some calculations. I want to modify the way the calculations are performed, for that I first need to understand ...
4
votes
2answers
2k views

Hight iowait while the wMB/s is low

I was indexing a MySQL table. It makes a high load on that computer. It seems due to a high iowait. But it also shows that the wMB/s is only 2.87. Isn't even a common SATA HDD able to handle more ...
3
votes
3answers
213 views

Changing the disk scheduler on the fly

Can the Linux disk scheduler be changed on the fly by writing to /sys/block/sda/queue/scheduler? Should applications (e.g. Mysql) be stopped / started when changing?
4
votes
5answers
373 views

performance monitoring

Is there some performace monitoring tool which would run in background gathering info about all system activity? Somethimes my system (Arch linux, 32 bit) slows down terribly and the top utility ...
4
votes
1answer
521 views

Does IO prioritise by the very nature of renicing a task?

The CFQ IO scheduler supports priorities though I am not sure that Deadline does (I believe not). The premise is that when I renice a task it gets a larger share of CPU under the Completely Fair ...
12
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5answers
28k views

How can I read line by line from a variable in bash?

I have a variable which contains multiline output of a command. What's the most effecient way to read the output line by line from the variable? For example: jobs="$(jobs)" if [ "$jobs" ]; then ...
7
votes
3answers
2k views

How can I monitor disk I/O in a particular directory?

I've got a few processes with a known name that all write to files in a single directory. I'd like to log the number of disk block reads and writes over a period (not just file access) to test whether ...
6
votes
2answers
6k views

Run process with higher priority

I want to run mplayer with higher priority than any other processes, including the IO-processes. How can I do that?
4
votes
1answer
521 views

“Split I/O”s on a Linux VM, disk alignment

I'm trying to figure out if there's some way I can tell if a system is being adversely affected by disk misalignment -- i.e. when I do a disk I/O operation, it actually needs to request extra blocks ...
13
votes
2answers
4k views

Why does high disk I/O reduce system responsiveness/performance?

I never quite understood why high disk I/O slowed the system so much. It's strange to me because I would expect the slow-down to affect only those processes dependent on the hard/optical drive data, ...
9
votes
1answer
1k views

What's the progress regarding improving system performance/responsiveness during high disk I/O?

Whenever there is high disk I/O, the system tends to be much slower and less responsive than usual. What's the progress on Linux kernel regarding this? Is this problem actively being worked on?
4
votes
3answers
785 views

How to get output from a remote shell

I have an application running on a server, started from the command line. From time to time, I need to connect to the server via SSH and get the output messages written to stdout from the application. ...
6
votes
3answers
687 views

Deleting lots of files

I accidentally created 8 million files and every time I'm trying to delete them the server almost dies because of the rm process eating all disk IO (the server is remote without console). Should ...
5
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1answer
1k views

How do I view the IO priority of a process?

How can I view the IO priority of a process? like to see for example if something has been ionice-ed.
5
votes
2answers
4k views

root user denied access to .gvfs in rsnapshot?

I was running rsnapshot as root and I got the following error. Why would this happen? what is .gvfs? rsnapshot weekly slave-iv ...
14
votes
2answers
2k views

Measure pipe throughput in the shell

There is a shell command that allows to measure how fast the data goes through it, so you can measure the speed of output of commands in a pipe. So instead of: $ somecommand | anothercommand you ...
35
votes
5answers
3k views

Redirecting stdout to a file you don't have write permission on

When you attempt to modify a file without having write permissions on it, you get an error: > touch /tmp/foo && sudo chown root /tmp/foo > echo test > /tmp/foo zsh: permission ...
8
votes
2answers
1k views

Heavy write activity on SSD nukes system performance

I've noticed that when I do heavy write applications, the whole system slows down. To test this further I ran this to do a (relatively) low-CPU, high disk activity: john -incremental > file_on_SSD ...
11
votes
1answer
521 views

How do I go about tracking down IO usage in Linux and other *nix OS'?

Occasionally, something on my system starts hammering the disk. I would like to log data that would let me know about I/O usage per process, then I could go back to it later and see what keeps doing ...
25
votes
12answers
2k views

How can I tweak my Linux desktop to be more responsive?

I have the experience that Linux works fine until the physical memory is exhausted. As soon as swap space is used the performance is severely degraded and the GUI becomes unresponsive. This problem ...