IO (or I/O) is an abbreviation for input/output, most commonly referring to disk input/output.

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High disk I/O activity in CentOS server

I have about 16 websites in a CentOS dedicated, and I am having some problems on high traffic hours, it seems to be a high disk I/O activity causing a general slowdown. I've installed atop and this ...
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1answer
34 views

99% disk IO spikes with Percona

So we have a server that has seemingly random spikes in disk I/O, going up to 99.x% at random times and for no obvious reason, staying high for ~1 hour, and then going back down. This hasn't been much ...
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20 views

What is the purpose of a ramdisk when fadvise exists?

My understanding is that fadvise will tell the system that the indicated files should be stored in the file system cache (RAM). What is the purpose of mounting a directory in a ramdisk when you can ...
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Is there a way to delete 100GB file on Linux without thrashing IO / load?

I have a huge log file I need to delete on a production web server. I'm worried it'll bring the system to a crawl if I rm it on Linux. Any brilliant ideas? Update: Filesystem: ext3 Partition: /var ...
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1answer
32 views

Does AWS EC2 have secondary disks scattered across the cluster?

I am using AWS EC2 Linux m3.xlarge to run a program called "Smart Information Retrieval System" which performs many I/O operations to/from the disk. I have tried running the same program on my laptop ...
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Why CPU spent time on IO(wa)?

I know wa (in top) measures the CPU time on waiting for I/O. Many articles say that. But I am confused that, based on 2 knowledge points: if a process uses a system call to read disk, the process ...
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3answers
447 views

Extremely High Hard Disk Reading Usage

My VPS configuration is as follows: H.D.D = 25GB RAM = 256MB OS : CentOS 5.5 I received an email from server provider showing that my VPS H.D.D read usage is 137GB in one day. I have installed ...
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5answers
652 views

Expected throughput when re-building RAID array?

I'm just doing some testing on a NAS RAID array we've been lent to see if we want to deploy it. Just to see whats what, I decided to see what kind of network performance we get when it's re-building a ...
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1answer
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htcacheclean doesn't seem to be cleaning the cache

I'm running mod_cache with apache 2 on a fairly high traffic'd site. I've set the htcacheclean to run in demon mode every 10 minutes to keep the cache at 4GB. It's currently at 15GB and doesn't seem ...
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1answer
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using temporary files vs pipes advantages and disadvantages

Say I have a file named jobs.csv and I would like to get the top 50k jobs done by Foo I can either do: # cat jobs.csv | sort -u | head -n 50000 > /tmp/jobs.csv # cat /tmp/jobs.csv | while read ...
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Benchmarking for DISK I/O Writes Per Second - ElasticSearch and MySQL

During working on our project we needed to decide should we use "ElasticSearch" or "MySQL" to record the audit/trail logs of the system. Searching speed is not an issue here, we needed to see the disk ...
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Are networks now faster than disks?

This is a software design question I used to work on the following rule for speed cache memory > memory > disk > network With each step being 5-10 times the previous step (e.g. cache ...
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2answers
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how do I know if an SSD reaches its performance capability?

I was monitoring a new db server with SSD RAID-10 installed. It works fine for now but I was worrying someday it could reach its capability as the business goes on. So how can I know that before it's ...
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5answers
241 views

High load due to I/O wait in Ubuntu 12.04 on EC2 instance

I am using Ubuntu server 12.04 , having trouble finding cause of load, I have seen change in response time of server from past week after reading Linux Troubleshooting, Part I: High Load It seems ...
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0answers
57 views

Restrict I/O Write usage using cgroups

I am trying to restrict I/O write usage on my server using cgroups. Here is my partition table info: major minor #blocks name 8 0 10485760 sda 8 1 9437184 sda1 8 ...
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1answer
56 views

How to disable search body in dovecot?

We run mail server of 30k e-mail accounts (Maildir) with Dovecot imap server. We suffer from high IO load, especially when a user starts to search large IMAP folders. Is any way of preventing search ...
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3answers
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Linux - How can I see what's waiting for disk IO

I have a server that has a really high load. Nothing is jumping out at me in terms of CPU usage, and it's not swapping. I think it's cause some processes are waiting for disk IO, and I want to see ...
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0answers
45 views

How efficient is the tac command on large files

The taccommand (catreversed) can be used to read a file backwards, just like cat reads it rom the beginning. I wonder, how efficient this is. Does it have to read the whole file from the beginning and ...
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kworker consuming +90% IO and zero disk write

this is a standard apache web server on AWS Linux AMI + EBS. We are noticing high load average (+8) and iotop -a shows: Total DISK READ: 0.00 B/s | Total DISK WRITE: 2.37 M/s TID PRIO USER ...
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1answer
53 views

6 GB/s SAS RAID 10 (6 Drive) vs. 3 GB/s SAS RAID 10 (14 Drive)

I am running MS SQL 2014 Standard and have a Dell MD 3000i iSCSI SAN. Rough specs: Dell R610 With PERC H700 controlling 6 x 2.5" 15K SAS drives (6 GB/s) Dell MD3000i with 14 x 3.5" 15K SAS drives ...
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2answers
77 views

Windows Server 2012 with SSD local drives — Random or Sequential I/O?

How can I determine where my Windows Server 2012 is using Random or Sequential I/O operations when writing/reading the local SSD storage? I have been asked to provide details to our hardware vendor ...
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2answers
41 views

How to find reason for hanging process (probably I/O related)

on Ubuntu 14.04 when I open a file browser or an "Open File" Dialog, the application hangs for about 5 to 10 seconds. I suspect this is due to some NFS requests. But how can I find out for sure? Is ...
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1answer
56 views

Disk I/O at limit with software raid

whenever I use rm or cp on a bigger file structure the disk i/o is going up to the top, but not with the focus on cp or rm, it is the software raid sync. My knowledge in this area is limited. The ...
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1answer
47 views

interpreting disk stats using sar

I have JBOD and Cassandra installed on it. I'm trying to figure out if my disk are totally free or they are boring. The sar -d result is in the end. As I understand until %util is low (less then 1) it ...
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MongoDB hogging IO but it doesn't show in mongotop or mongostat

Iotop says mongod is using a lot of IO (96.32%) for a long while but mongotop and mongostat show a bunch of zeros. How can I better monitor mongodb and find out what's happening?
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445 views

How to reduce I/O on EC2 micro instance running wordpress

I have been running a very small wordpress site on Amazon EC2 for about 2 months, using the free tier micro instance. I have been getting billed a few dollars each month for going over the disk I/O ...
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38 views

IO Rate is exceedingly incrementing

I have read through Is a 'high' IO rate healthy?, and was at ease when I read someone say that even 50,000 / hr wasn't an issue.... or not unhealthy, to answer their question; so I increased ...
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1answer
62 views

IO tasks easily starve eachother on 3Ware 9650SE

I have a server (Debian 6 LTS) with a 3Ware 9650 SE RAID controller. There are two arrays, one RAID1, one RAID6. It runs Xen 4.0, with about 18 DomUs. The problem is that I experience that IO tasks ...
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44 views

Can poor Internet connection affect the IO read on my server?

I'm trying to spot the culprit causing too much IO read in my server. Issuing IOTOP -ao I have come accross many httpd processes among which one caught my attention: PRIO USER DISK READ ...
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1answer
67 views

How can I monitor disk IO load on a Windows 2008 server?

We are running multiple processes on our servers, which are mostly CPU intensive, but also use the local HDDs for reading the data. I can trivially look at the CPU load and memory usage in TaskManager ...
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1answer
79 views

gstat output on FreeBSD: does it show an average over time?

When you run the gstat command on FreeBSD to get information about i/o performance, you can pass the -I (interval) option to change the default interval from 1 sec to some other time frame. My ...
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1answer
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How to save iotop's output for a specific period of time

I am trying to discern what processes are making huge Read/Writes on my server disk. I know I can use iotop -ao but is there a way I can save iotop's output for a specific period of time to study ...
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2answers
45 views

What is the difference between truss -D and truss -E?

I am currently analyzing a command on Solaris that reads from a file and has very low performance. The truss -D commands shows me read system calls taking up to 0.03 seconds, but when I use truss -E, ...
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404 views

Evaluating the CPU I/O wait on Linux

Doing a top to check the io wait, I get these figures: Cpu(s): 6.7%us, 1.4%sy, 1.2%ni, 85.5%id, 5.0%wa, 0.0%hi, 0.3%si, 0.0%st Looking at these figures (%us ~= %wa), do they mean that: ...
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7answers
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Can anyone explain precisely what IOWait is?

As much as I have read about iowait, it is still mystery to me. I know it's the time spent by the CPU waiting for a IO operations to complete, but what kind of IO operations precisely? What I am also ...
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VPS Unknown Read/Write [closed]

I had an lfd email alert - I have installed CSF - today revealing that my server (Centos 6.6) has been using a lot of server resources for 5 minutes. I checked my VPS graphs and noticed that my ...
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2answers
358 views

How to figure out which processes are deleting files from a specific directory?

I'm trying to figure out which processes are deleting files from a specific directory, so I want to set up and run auditd on my system. I've set up the following rule in audit.rules: -w S unlink -S ...
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1answer
548 views

How to check which processes are deleting files without using inotify or auditd? [closed]

I'm trying to figure out which processes are deleting files from a specific directory on my CentOS server. I looked at inotify, but all this does is to tell me how many file deletions are occurring; ...
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1answer
157 views

rrdgraph generation fails on high IO load

We have a 4 core CPU production system which does a lot of cronjobs , having constant proc queue and an usual load of ~1.5. During night time we do some IO intensive stuff with postgres. We generate ...
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4answers
874 views

Changing the I/O scheduler for a specific disk

I would like to change permanently the I/O scheduler for a specific disk on Fedora 20. According to what I have found, this can be achieved by executing the following shell line as root: echo ...
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6answers
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I/O Performance Benchmarking Linux

Just finished setting up a poor mans SAN with iSCSI and want to benchmark it. What are some good I/O performance benchmarks for Linux besides: hdparm -tT /dev/sda1 How do I get a IOPS measurement? ...
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2answers
396 views

IOMeter showing hardly any data

I ran IOmeter on a Windows Server 2008 R2 SP1 server for 18 hours and when I clicked on "Stop current Test and Save Results" it stopped the worker processes (I only had 1). When looking at the ...
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1answer
66 views

how to find cause of io spike

Everyday at around the same time, the IO usage on the server where our mysql slave goes up to 100%. I have setup a script that takes IO information every five minutes so I can find out why this ...
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11answers
7k views

What creates CPU I/O wait but no disk operations?

I have CPU I/O wait steady around 50%, but when I run iostat 1 it shows little to no disk activity. What causes wait without iops? NOTE: There no NFS or FUSE filesystems here, but it is using Xen ...
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0answers
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“Nosy Neighbor” and the CFQ scheduler

I'm trying to understand how does using CFQ affects the "Nosy Neighbor" problem. I'll ask it a bit naively, can a "Nosy Neighbor" even exist when using CFQ? Isn't that CFQ should make sure all ...
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2answers
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Beyond 1Gb upload on a single linux server

I have a high hit nginx web server on CentOS that provides static large content. when the number concurrent connection are low, server could easily provide up to 4Gb of traffic , but when the number ...
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1answer
198 views

Does changing /sys/block/sda/queue settings take effect immediately?

How long does it take for changes to the following settings to take effect: /sys/block/sda/queue/scheduler /sys/block/sda/queue/rotational /sys/block/sda/queue/read_ahead_kb Is it ...
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1answer
360 views

Innodb performs IO Operation when idle

I am currently doing some stress testing where I am pushing inserts to the database as fast as I can. The simulation inserts 10000 records per second. After inserting around 200 million records I ...
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1answer
576 views

Quantifying the effects of partition mis-alignment

I'm experiencing some significant performance issues on an NFS server. I've been reading up a bit on partition alignment, and I think I have my partitions mis-aligned. I can't find anything that ...
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2answers
3k views

Issues with Server 2012 using DFSR running on Hyper-V 2012

We have a number of Server 2012 systems, all of which run virtualised on Hyper-V 2012 server. We are having problems with two such virtual instances, both of which are used as file servers, whereby ...