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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How to set up ZFS with ZIL and L2ARC SSD?

I have been considering bcache and flashcache. However my friend suggested me something called ZFS. In fact it says that formating disk with ZFS can actually do the exact same thing without kernel ...
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Storing thousands of files in one directory

I have a web-site that I'm checking for performance issues and bugs, and i came across a caching code that caches thousands of files into one single directory. I understand that this is not good and ...
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Why is I/O uninterruptible?

What is the rationale behind making I/O uninterruptible? What would be the negative consequences if a process handling I/O were allowed to handle a signal?
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How to improve IO when there is a lot of random read and write?

My scripts uses tons of read and writes. Most of them are small and random. I want Linux to wait 10 seconds before writing any data to the disk. How would this be achieved? I think Linux can already ...
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Does linux have something like supercache?

I installed http://www.superspeed.com/desktop/supercache.php for windows and the result is awesome. Every program I run is faster. Basically it uses the memory to cache data. Simple idea. I also use ...
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Strange IOStat xk. Moving a mere 40GB data is too slow. Can anyone explain?

iostat -xk 5 avg-cpu: %user %nice %system %iowait %steal %idle 0.99 0.00 1.10 11.01 0.00 86.89 Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s ...
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220 views

is writing to slow storage in nohup mode blocking the process?

If I have a process writing to nohup and the storage where it writes to is slow, does it block the process which is running in nohup? For example: process A is running in nohup, it needs to write 10 ...
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IOStat report large ocassional writes but find reports no big file

root@host [/home4]# find . -type f -size +2000k -exec ls -lh {} \; | awk '{ print $9 ": " $5 }' ...
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How to know recently updated files

If I run iostat -x 1 I saw ocassionally large 5MB to 10MB writes. What files are being written? I want to check the recently created files with size over 5MB for example. How would I do so?
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204 views

iostat report huge writes to drives that's not even mounted

root@host [~]# fsck /home2 fsck from util-linux-ng 2.17.2 e2fsck 1.41.12 (17-May-2010) /dev/sdb1: clean, 6018617/91578368 files, 54524459/366284000 blocks root@host [~]# fsck /home4 fsck from ...
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Which drive had a “journal commit I/O error”?

I received a message: kernel:[123456.789012] journal commit I/O error Which disk drive had the journal error?
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Determine which process is taking most of disk bandwidth?

When the HDD indicator is blinking (for a long period), how could I know which process is taking most disk bandwidth?
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140 views

Does symlinking from Drive A to Drive B affect I/O on Drive A?

I was wondering if IO through a symbolic link affects IO on the host drive even if it points to a seperate drive? My setup is, /dev/sdb2 1.8T 443G 1.3T 26% /home1 /dev/sda3 1.8T 1.7T ...
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2k views

Meaning of colours in htop

Given the option: [ ] Detailed CPU time (System/IO-Wait/Hard-IRQ/Soft-IRQ/Steal/Guest) In htop (Version 1.0.1) what are the meanings of the colours? In the following image, I'm seeing rather a lot ...
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1answer
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I/O error but no bad block is reported in syslog

I got errors like this in my syslog, but there's no bad block or sector defined in kernel report, I can't just replace the HDD right now and I prefer to reallocate the bad blocks for now, so I need ...
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Can I watch the progress of a `sync` operation?

I've copied a large file to a USB disk mounted on a Linux system with async. This returns to a command prompt relatively quickly, but when I type sync, of course, it all has to go to disk, and that ...
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How to Throttle per process I/O to a max limit?

I'm looking for a way to limit a processes disk io to a set speed limit. Ideally the program would work similar to this: $ limitio --pid 32423 --write-limit 1M Limiting process 32423 to 1 megabyte ...
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1answer
135 views

What is the difference between > and >> (especially as it relates to use with the cat program)?

Suppose that I have a file called temp.txt. Using the cat program, I would like to add the contents of this file to the end of myfile.txt -- creating myfile.txt if it does not exist and appending to ...
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752 views

What keeps one side of an rsync so busy?

I've got a debian machine in my lan serving as a backup server for the others. It has four HDDs combined into a software RAID 5 md device, on that an lvm, and on that a btrfs. Backups are made using ...
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328 views

Running jobs in parallel on Ubuntu - I/O contention differences between Perl and Java

Apologies if this is off topic - it concerns the relative efficiencies of running I/O-heavy Perl/Java scripts in parallel on a Ubuntu system. I have written two simple versions of a file copy script ...
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382 views

File size of 60.0 PB is wrong. Can deleting it cause data loss?

While backing up some data (a 200 GB home directory) with rsync, I got an I/0 error for a particular file, after which rsync continued on "normally" with its backup. The problem source file showed as ...
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494 views

How can I read lines at a fixed speed?

I need to read a large log file and send it over a local network using (netbsd) netcat between two VMs on the same host workstation. I know that netcat has an interval, but as far as I can tell, the ...
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940 views

Portability of “> /dev/stdout”

Occasionally I need to specify a "path-equivalent" of one of the standard IO streams (stdin, stdout, stderr). Since 99% of the time I work with Linux, I just prepend /dev/ to get /dev/stdin, etc., ...
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script for logging all the stats for a particular process

I want to monitor CPU usage, disk read/write usage for a particular process, say ./myprocess. To monitor CPU top command seems to be a nice option and for read and write iotop seems to be a handy ...
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781 views

I/O statistics per user

I have access to an academic supercomputer where there is an NFS filesystem where our lab keeps our data. When I run iostats -nh I believe I am getting statistics for all users accessing all storage ...
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235 views

How do I record disk performance on slow hardware and then replay it to faster hardware and benchmark it?

I am currently performing various development tasks that are slow on my current system because of IO performance. Is there a way to record disk operations while performing IO consuming tasks, ...
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How can I limit the output speed of stdout?

I'm running CentOS 5.7 and I have a backup utility that has the option of dumping its backup file to stdout. The backup file is rather large (multiple gigabytes). The target is an SSHFS filesystem. To ...
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Write inside a socket open by another process in Linux

Is it possible on Linux for a process to write inside a socket open by another one? Let's say I open a connection to google.com using netcat: myuser@linux:~$ nc google.com 80 Now I can lookup for ...
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vmstat IO stats: why the high bo during a download?

On my RHEL 4 machine, I was downloading a huge file (2.5GB)..I was checking the output of vmstat and was especially curious about seeing the disk IO using bi and bo. I know iostat is a better tool ...
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346 views

Mysterious write IO

I am just reviewing the disk IO of a XEN VM server. I stumbled across a DomU that has constant write traffic. To narrow that traffic further down I logged in to the DomU (CentOS 5, 64 Bit) and ...
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SysBench highlighting abysmal disk write performance on white box vs Tier1 server

Have been testing white box system with SuperMicro X8DTL motherboard with various SATA hard disks such as 7,200RPM Seagate Constellation ES and 10,000 RPM Western Digital VelociRaptor. Have tested ...
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100.0%sy with poor disk performance

I have RHEL 5.4 kernel 2.6.18-164.el5 and I am experiencing very bad disk performance that happens randomly during working with Oracle. Nothing appears in the logs. When it happens, I see one CPU ...
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Copying a file that is written at the same time

This related question can't solve my exact problem, so I'm writing a similar question. My scenario is the following: a program (run by wine) writes to a file sized about 10-500 KB. About 1 KB ...
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116 views

In terminal, I can search to end of log faster than the data gets there

[The Question] Is there some way to have the pipe/tee/write combo write lines immediately? ... if it can be done, what is the trade-off? [The Backdrop] My script sends a keypress to the terminal, ...
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dealing with un-executable commands inside a shell-script

I am given an assignment like this: Write a Bash script that takes a *.tex file as command-line argument and checks if the file executes correctly without any errors. If it executes without any error ...
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830 views

Why do backgrounded processes sometimes stop spontaneously?

Sometimes, some time after I've backgrounded a process with bg in bash, when I press Enter in the same shell to redisplay the prompt (just to check that I'm still in bash when some output from the ...
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GNU/Linux, IO performance problems

I have some problems with my system performance. As I was adviced here, I used sar: $sar -u 5 and found out that the problems are caused by a low HDD performance, as I supposed (high %iowait). ...
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Make iotop show only the most disk-intensive item

My laptop (no VM, just plain Ubuntu with encrypted home) freezes for 3 minutes a few times per day. During these 3 minutes, the disk LED indicates intense disk activity, and I can't even move the ...
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Which root paths should reside on fast media?

Which paths under / should be mounted on fast media, and which can be mounted on slower media without significantly affecting system performance? My guess: Fast Partition: swap (2G) Partition: ...
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433 views

Utility to buffer an unbounded amount of data in a pipeline?

Is there a utility that I can stick in a pipeline to decouple read and write speeds? $ producer | buf | consumer Basically, I want a utility buf that reads its input as fast as possible, storing it ...
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159 views

Repeatably generate a read error for testing? [duplicate]

I'm trying to test the error handling in some software, in particular what happens when an error occurs reading from a file or pipe. Is there a simple way to send a certain amount of data to stdout ...
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1answer
329 views

BluRay Burner High I/O Wait State with UDF; Optimization Possible?

I've recently scaled back my home network, with one of the bigger changes being a switch-over to using a BD-RE drive for backup. With years of pictures and home video consuming about 25GB, and ...
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287 views

Removing redirection operator does not change output. Why?

I saw this usage of redirection somewhere, and thought it was a typo: grep root < /etc/passwd But after I run it, I saw that it gives the same output with grep root /etc/passwd: $ grep root ...
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1answer
515 views

iostat usage and output

When I run the iostat command like this: iostat -d I get a result something like this: Linux 2.6.18-238.el5 (mon01) 09/03/2011 Device: tps Blk_read/s Blk_wrtn/s Blk_read ...
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How can I specify that curl (via command line) overwrites a file if it already exists?

I'm using curl in this syntax: curl -o myfile.jpg http://mysite.com/myfile.jpg If I run this command twice, I get two files: myfile.jpg myfile-1.jpg How can I tell CURL that I want it to ...
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copy consumed output to stdout when stdout is redirected to a file

Given a command the output of which is being processed by, for example, grep I also want the actual output to be included in the log file for debugging purposes. For example if I have the following ...
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How race conditions affect reads and writes (that happen at the same time)

Let's say I open a file a for reading. What if an application, let's call it aWriter writes to this file in random intervals. Are there any possibilities of me receiving improper file contents if I ...
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866 views

Measuring disk I/O usage of a program

time is a brilliant command if you want to figure out how much CPU time a given command takes. I am looking for something similar that can measure the disk I/O of the program and any children. ...
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How to stop xargs from badly merging output from multiple processes?

I'm using xargs with the option --max-args=0 (alternatively -P 0). However, the output of the processes is merged into the stdout stream without regard for proper line separation. So I'll often end ...
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530 views

Piping output from a segfaulting program

I have a script that calls a program (specifically, ttf2afm, part of tetex 3.0) that sometimes segfaults and sometimes doesn't. The information I need is always printed out before it segfaults, but ...