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

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How to keep md-raid from blocking IO?

I run a server with md-raid (software) level 1 (2 HDDs mirroring) and several different applications run on it. The problem arises when file-intensive jobs (e.g. extracting large archives) run while ...
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18 views

Improving I/O rates for EBS snapshot backed volumes

I'm working with a system that takes a set of 42 rotating daily EBS snapshots of each of its numerous (40) volumes for disaster recovery purposes. EBS volumes are aggregated into a RAID volume. A set ...
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31 views

How can I determine which files have high I/O in Windows?

In trying to reduce the storage bottleneck on a Windows server (2008 R2) I need to find the files that have the highest I/O over a long period of time (aka 'hot' files) so I can move those to SSD ...
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40 views

Disk IO Rate: What causes it and what does it mean to me?

I just got a mail from Linode saying that my account "has exceeded the notification threshold (1000) for disk io rate by averaging 1017.36 for the last 2 hours. " My question is just out of curious: ...
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42 views

Filesystem Performance for LUKS Encrypted Volumes?

As you can format a LUKS volume with any filesystem you want, are certain filesystems better-suited to IO performance against an encrypted filesystem? Specifically, I'm wondering about a loop device ...
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68 views

What are front merges in I/O scheduling and how can I tune this parameter?

My Linux uses the Deadline algorithm for I/O scheduling. One of the parameters is the front_merges parameter under /sys/block/sda/queue/iosched/front_merges. By default it is set to 1, which means ...
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29 views

Check If I/O causing high load average

I wants to understand how to measure if I/O is causing load average high and how to calculate optimal and critical I/O value. Because sometime there is a load spike on my server but other ...
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71 views

How I can reduce disk IO in MySQL 5.6.26?

I was using MySQL version 5.1.52 for my application but recently I have updated it to 5.6.26, but now I am facing very high disk IO. Following are system configuration: OS : Linux 2.6.39.4 RAM : ...
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128 views

Acceptable I/O speeds for 6 x 250GB SSDs in RAID 10

I'm running CentOS 7 (XFS filesystem) on a dell server with a PERC H700 raid controller. Inside this server I have 6 x Samsung 850 Evo 250GB SSDs (yes they are consumer drives however, this is a home ...
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98 views

KVM bad IO sync performance in Linux guest

I'm setting up virtualized Ubuntu 15.10 guest inside Ubuntu 15.04 server using libvirt and KVM. Storage in host system: # mount | grep ext4 /dev/sda1 on / type ext4 ...
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40 views

How to find the bottleneck for slow rsync

I want to find the bottleneck for a slow rsync. I see these parts (on byte flow order): IO on source CPU on source Network CPU on destination IO on destination How can I debug this?
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28 views

collectl vs strace - reported block io read/write size

I've got an xfs mount with standard settings (it's an AWS host): [root@host ~]# xfs_info /dev/xvda1 meta-data=/dev/xvda1 isize=256 agcount=4, agsize=524224 blks = ...
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Long Response Times for Reads via FCoE

We're getting some intriguing performance with our new FCoE environment, and I was hoping that people could let me know if what we're seeing is expected behaviour. Our switching environment consists ...
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68 views

How can I debug: iostat shows 100 util but there's 0 read or write in iotop

The server is an AWS EC2 instance. Ubuntu 14.04.2 LTS. I have an EBS (xvdf is the device name) mounted to the instance. And this is the problem drive. From iostat I see that drive is 100% utilized ...
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48 views

How to check what is causing performance issue

[Edit] This question is different than what is suggested by the moderator, I am trying to find out what could have caused the API to become slow because of the few lines of codes. I am not trying to ...
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40 views

How to ensure that I/O requests have returned to a normal rate?

On Amazon Web Services I am using a t2.small EC2 instance as a VPS serving a few websites on a LAMP (PHP) stack. I was just hit with a bill which almost triples my usual bill. I see that my I/O ...
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114 views

Starting PHP session sometimes take very long time

Sometime ago we have came upon interesting problem. Sometime (not everytime, lets pretend nearly each 100-200 hit) session_start() takes very long time. Up to 60 seconds. (longest one was 63, ...
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32 views

How many milliseconds of await is considered to be high? [closed]

How many milliseconds of await is considered to be high? i have 800ms and 600ms iostat -x avg-cpu: %user %nice %system %iowait %steal %idle 1.28 0.00 0.22 0.90 0.00 ...
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16 views

Get NewRelic to respect ionice'd processes

On our web server, we perform an incremental backup of our files every 4 hours using rsnapshot. To perform the actual copying of files, I've configured it to use a custom script, cp-nice that has the ...
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55 views

Most side effect-free way to archive a large file while it is being modified

I am looking after an application that generates a large amount of data in a log file (about 5G a day) on a Red Hat server. This process runs for 24 hours during the week, so there is no point in the ...
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86 views

Redis parent process smashing disk despite appendfsync = no

We are seeing loads of IO from redis-server despite our save operations being set to occur once every 15 minutes only. The workload is a "full page cache"; we store blobs of compressed HTML. The HTML ...
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49 views

Ubuntu 12.04 high io by root process

Ubuntu server 12.04. Installed on hdd disk. There is postgresql database on server runing on other ssd disk. The problem is in high io by some root process on hdd disk. iotop shows 2 processes with ...
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Ubuntu CPU I/O Rate Spike

Getting really crazy spikes today on a Ubuntu server for CPU / IO. CPU Chart is showing as much as 210% CPU usage - no idea how that is possible. IO has gone as high as 11912. (Usually well under ...
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299 views

Finding correct IOPS to set limit with ESXi 5.5u2 and vSphere

We're running an ESXi 5.5u2 hypervisor that has a mirror of 2 15k SAS drives with a couple of VMs inside and we noticed some services become briefly unreachable if another VM is using all the IO. So ...
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89 views

DRBD high iowait every 65 seconds

I have a peculiar problem: simple INSERT queries to MySQL slow down and appear in my slow q logs every 65 seconds exactly. My stack looks like: mysql56u (IUS) on CentOS over ext4 over drbd over ...
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41 views

Sustained io testing linux

I wish to hammer the io of some disks for an extended period of time and become aware whenever I can't read from a block (or some other symptom letting me know of an issue with backend storage). There ...
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30 views

Is “'Light-Speed' Disk Access” really a thing? [closed]

I just saw an advert for Hyve hosting on You Tube. One statement made me curious, they said they offer "'Light-Speed' Disk Access": Is this just a fancy way of saying they have optical technology, ...
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79 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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254 views

Does Linux, Apache HTTPD or PHP cache frequently / recently accessed files?

Let's say we have a simple index.php file that goes: <?php inclde('file1.php'); inclde('file2.php'); inclde('file3.php'); Presumably, this will ultimately result in three additional ...
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319 views

I/O and RAM limitations are important for Hadoop performance. But is disk speed related to I/O?

Hortonworks says this: "Most often performance of a Hadoop cluster will not be constrained by disk speed – I/O and RAM limitations will be more important." * How is disk speed not related to I/O ...
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Virtual machines and I/O heavy workload, is it ever sane?

I have seen on numerous virtualization services (Azure) and products (vmware,kvm,hyperv) I/O and system stalls under heavy I/O workload. My questions are: Is it ever sane to use a Virtualized ...
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428 views

No Space left on device after Jenkins installation

Is there any reason i would get a 'No space left on device" error on mkdir. I have confirmed that i have enough space left. around 68% is free. and also i have 1% iNodes consumed. This is CentOS 7 ...
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132 views

mdadm and LVM high load and IOwait

I've got a new CentOS 6.6 server with 2 HDD with mdadm & LVM. As I've used the CentOS install CD I assume everything should be aligned properly. I've just written a KVM image to a LVM LV using dd ...
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185 views

What it means when Linux has no I/O scheduler

I have some virtual machines running Ubuntu cloud-based image 14.04-1 LTS version. I wanted to see the IO performance of different IO schedulers on the VM so I went to ...
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252 views

PHP-FPM Stuck & High IO

Actually on my mutual hosting server I'm using PHP 5.6.3 with one pool. Sometimes, my php-fpm process is stuck with 50% of WA and I can't kill it, I can't even restart my VM. I'm using 245MB/3968MB, ...
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72 views

ubuntu kvm disk io slowdown after some tyme

Host system: Ubuntu Server x64 12.04 mdadm raid 1 (/dev/sda /dev/sdb) no lvm dd bs=1M count=256 if=/dev/zero of=filename conv=fdatasync avarage ~ 40 MB/s NCQ on disks is disabled WriteCache is ...
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97 views

MySQL slow file I/O

I got a little issue with MySQL having slow file IO. When benchmarking 1k blocks (I did them on purpose that small for worst-case) I get an hdd speed of about 2MB/s. When looking at iotop while ...
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54 views

how to find the highest IO consumer on a disk? [closed]

Can some one help to find highest IO consumer on each individual disks? i.e Which process consumes the most IO on /dev/sda, the highest IO consumer on /dev/sdb etc.
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File IO being slow

I've rented this root server with a RAID1 mdadm software raid setup. Using dd to benchmark the file IO speed it achieves 230MB/s write (default blocksize). Certain tasks such as mysql are way slower, ...
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95 views

how to check if a process with heavy io usage is running properly

I am now managing a computer cluster for scientific computing. Some processes in the cluster need heavy io usage. Now I find such a process: Its state changes rapidly between DOWN and RUN and its ...
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66 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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358 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 a while, and then going back down. This didn't use to be ...
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41 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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2k views

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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259 views

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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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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177 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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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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144 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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114 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 ...