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Questions tagged [iostat]

The iostat command is used for monitoring the CPU utilization and input/output load of devices attached to a system by observing the time the devices are active in relation to their average transfer rates.

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Linux kernel phantom reads

Why if i write to a raw hard disk (without FS) the kernel also makes reads. $ sudo dd if=/dev/zero of=/dev/sda bs=32k count=1 oflag=direct status=none $ iostat -xc 1 /dev/sda | grep -E &...
Alex's user avatar
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Is there iostat-similar tool that tracks swap area activity and page cache miss?

The iostat tool is able to tell us cpu usage, disk r/w throughput second-by-second. Is there a similar tool to track swap area activity and page cache miss? For example, the tool should tell us the ...
Dachuan Huang's user avatar
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iostat returns disk utilization greater than 100% while profiling a Beaglebone Black board

I need to profile the performance of software running on a BeagleBone Black (BBB). The BBB has an ARM Cortex-A8 up to 1GHz frequency, 512MB RAM, and 4GB eMMC onboard flash storage. You can find more ...
vnzstc's user avatar
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Our MySQL is read heavy, but iostat reports that almost no reads are taking place. How come?

According to MySQL's STATUS command, we have about 500 reads and ~20 writes to our DB per second. But iostat is reporting that ~70 writes (w/s) and ~0.5 reads (r/s) are taking place on the ...
edmz's user avatar
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How can I monitor whether disk activity is sychronous or asynchronous?

My Google-fu simply cannot find an answer to this. If I have a process with heavy I/O activity, how can I check whether it's using asynchronous or synchronous writes? (I want this information to ...
sssheridan's user avatar
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degraded iops and throughput on a linux machine in a cluster

we have a linux-based cluster on AWS with 8 workers. OS version (taken from /proc/version) is: Linux version 5.4.0-1029-aws (buildd@lcy01-amd64-021) (gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)) #...
Elad Eldor's user avatar
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2 answers
2k views

In iostat, why are kB_wrtn/s and kB_wrtn the same?

/dev/sdc is a SATA hard drive. Do the kB_read and kB_wrtn fields sometimes, in some situations, show total counts? Here it seems to be just the same as the per second value. Linux kernel 5.4.0-26-...
brendan's user avatar
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643 views

Process shows as 100% I/O bound while producing minimal disk activity, disk util is at 100%

We are having quite strange problem. There is a program (cryptocurrency node to be precise) which has local database of all the transactions ever made. Database is huge - around 15 TB. The problem is ...
DimaA6_ABC's user avatar
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2 answers
501 views

How do I get the linux kernel to track io stats to a block device I create in a loadable module?

I've been looking and looking and everybody explains the /proc/diskstats file, but nobody seems to explain where that data comes from. I found this comment: Just remember that /proc/diskstats is ...
stu's user avatar
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Does IOSTATS show output since boot or since last execution?

I see conflicting information online about use of IOSTAT. In particular I would like to be able to show an average since boot. Based on information I have read if I have never issued the command ...
barrypicker's user avatar
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Understanding iostat block measurements

I am trying to understand how data is written to the disk. I'm writing data with dd using various block sizes, but it looks like the disk is always getting hit with the same size blocks, according to ...
Elliott B's user avatar
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How to find which disk is being written to/read from in an LSI HW RAID logical volume?

On this system there is a lot of "await" which is causing slow response. i need to find out which disk behind the LSI logical volume is slowing it down... IBM blade, 2 HDD with LSI RAID (LV simple ...
rajeev's user avatar
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Why is the size of my IO requests being limited, to about 512K?

I read /dev/sda using a 1MiB block size. Linux seems to limit the IO requests to 512KiB an average size of 512KiB. What is happening here? Is there a configuration option for this behaviour? $ ...
sourcejedi's user avatar
2 votes
2 answers
3k views

NVMe disk shows 80% io utilization, partitions show 0% io utilization

I have a CentOS 7 server (kernel 3.10.0-957.12.1.el7.x86_64) with 2 NVMe disks with the following setup: # lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT nvme0n1 259:0 0 477G 0 ...
mike's user avatar
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IO wait time is higher than disk utilization. Isn't this impossible? [duplicate]

I am trying to improve my understanding, following this (so far) unanswered question: Possible limiting factor during upgrade of Fedora VM - not disk or cpu or network? I ran the following test load, ...
sourcejedi's user avatar
4 votes
3 answers
2k views

iostat: avoid displaying loop devices information

Given the annoying feature of snap's loop devices, my iostat output in an Ubuntu 18.04.02 is kind of like this Is there a way to filter out loop devices other than | grep -v loop ? $ iostat -xm ...
pkaramol's user avatar
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How to find max queue length for device?

Recently I ran into some I/O overload problrms on some of our machines and I have been searching to find thresholds for some metrics like: avgqu-sz await svctm Then I saw this post on Stack ...
BlackCrystal's user avatar
1 vote
1 answer
239 views

What does "no device" mean when running iostat -En

We presume to have a faulty cable that connects the SAN to a direct I/O LDOM. This is a snippet of the error when running iostat -En c5t60060E8007C50E000030C50E00001067d0 Soft Errors: 0 Hard ...
hovey's user avatar
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How to get Disk Stats based on different parameters

Is there any way to get a disk stats grouped on certain params like: writes by size/latency? reads by size/latency? something like: total writes - 100 writes by size: - < 4096 - 20 - ...
Manish Gupta's user avatar
3 votes
1 answer
3k views

Disk io stat “averaged” over a period of time

I am using the iostat utility on my RedHat Linux server to monitor the performance of a disk. When I use "iostat -xd sdh 1", I get the perf result printed every one second. When I use "iostat -xd sdh ...
Ahmed's user avatar
  • 31
5 votes
1 answer
4k views

iostat: what is exactly the concept of merge

From iostat man pages: rrqm/s The number of read requests merged per second that were queued to the device. wrqm/s The number of write requests merged per second that were queued to the device. r/...
pkaramol's user avatar
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How can I remove the headers

I would like to remove both headers (that are incidentally repeated). Any solution for it? [root@report]# iostat -xd 5 Linux 3.10.0-693.21.1.el7.x86_64 (mdds-pgbackup-01) 07/05/2018 _x86_64_ ...
Fayne's user avatar
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4 votes
1 answer
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Linux - Extracting Tar dramatically slows down server

I have a web server (specs below) with 12 TB of storage. I am moving massive amounts of csv files packaged in TAR's to the server, then extracting on the server. The problem is that when extracting ...
lessharm's user avatar
0 votes
1 answer
1k views

Reading iostat utilization with ZFS zvols

First off, I asked this question 5 days ago over on Serverfault. I hope I'm not doing a bad by bringing it over here to the Unix&Linux Stack. I have also asked this question on 3 other sites not ...
user246270's user avatar
1 vote
1 answer
1k views

how to query sar(sysstat) for more than one day data points

I don't see 'sar' command accepts date-and-time as starttime(-s) or endtime(-e) than just time. So, how to query 'sar' for more than one day's data point with older date and times(-f not going to help ...
Murali Mopuru's user avatar
0 votes
2 answers
819 views

Remove system information from iostat command output

I am trying to get some I/O stats about the partitions on the system using iostat command as follows: iostat -d /dev/sda The output appears as follows: Linux 4.10.0-33-generic (test) Tuesday 26 ...
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Track total data written in and read from a folder within bash script

I have a bash script to do calculation. This calculation generates big scratch files as big as 12 GB and the disk usage of scratch folder is ~30 GB. I want to know how much total data is written to ...
ankit7540's user avatar
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How to find process doing very high io read (without iotop)

By using iostat I see a constant 200+MB/s read on a certain device. How can I understand on CentOS which process is causing this, without using iotop (I cannot install it in this environment)?
kuma's user avatar
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7 votes
1 answer
1k views

why linux cp command don't consume disk IO?

os: centos7 test file: a.txt 1.2G monitor command: iostat -xdm 1 The first scene: cp a.txt b.txt #b.txt is not exist The second scene: cp a.txt b.txt #b.txt is exist Why the first ...
tairyao's user avatar
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0 answers
182 views

What is the difference between nfs_readpage and nfs_read?

Does every nfs_read always has a nfs_readpage request or does both are exclusive? Please explain. I am trying to understand this: http://www.fsl.cs.stonybrook.edu/~mchen/mountstat-format.txt
GP92's user avatar
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2 votes
0 answers
551 views

Priority read and write files

Good day, I had a question that I could not find the answer. I tested my hard drive, mounted on /media/data using dd. Some simple scripts: write: echo "3" > /proc/sys/vm/drop_caches for i in {1....
scmb's user avatar
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1 vote
0 answers
744 views

iostat disk utilization is full when there is no IO happening

I'm doing iostat on RHEL-6.6 machine and the results shown by 2 columns are difficult to understand. iostat -xm 1 result: avgqu-sz = a large number (42353468) %util = 100% There is absolutely no ...
Bhaskar Jupudi's user avatar
1 vote
1 answer
6k views

Install IOTOP/IOSTAT via ZYPPER (or anything else) on a SUSE (SLES) 12 Virual Machine (HyperV)

I have a virtual machine hosted on HyperV. It is a SUSE Enterprise 12 OS residing in a rack somewhere in the dark side of our office. This machine is under-performing during a certain load that takes ...
DraxDomax's user avatar
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4 votes
1 answer
797 views

Is there a way to monitor disk i/o patterns? (i.e. random or sequential i/o?)

While an application is running, I can monitor disk bandwidth usage using linux tools including dstat. Now I'd like to know how many sequential or random disk I/Os are occurring in the system. Does ...
syko's user avatar
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8 votes
1 answer
12k views

Execute command inside guest vm Libvirt

Is it possible to execute a command for eg:iostat inside a guest VM using libvirt or virsh .I want to find out IOPS for a guest vm but with libvirt java api I am not able to get the IOPS of a vm ,...
arpit joshi's user avatar
1 vote
0 answers
393 views

Random write on DISK benchmark shows high read rate on iostat

I am running a random write benchmark directly on some disks (HDD & SDD) and I am getting some weird output data on the iostat monitor. Besides the usual write rate, there is a read rate that I ...
Gustavo Portela's user avatar
0 votes
1 answer
308 views

Getting averageReadTime and averageWriteTime in solaris(disk I/O)

I am working on getting 'Average read time (ms)' and 'Average write time(ms)' from "iostat -xnp" command. In linux there is a '/proc/diskstats" command, which gives me 'Time spent in reading millis' ...
Venkat Teki's user avatar
7 votes
1 answer
14k views

iostat - What does the 'steal' field mean?

In output of iostat there is a steal field, according to man page the field is used to: Show the percentage of time spent in involuntary wait by the virtual CPU or CPUs while the hypervisor was ...
Eric's user avatar
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4 votes
0 answers
426 views

IOSTAT report doesn't match with DD benchmark

I am running a DD benchmark but the obtained results are not matching with the IOSTAT values. This is the DD sample: $ sudo dd bs=4096 count=690 if=/dev/zero of=/mnt/tmp/test oflag=dsync 690+0 ...
Gustavo Portela's user avatar
8 votes
2 answers
49k views

where can I find the disk latency using iostat ( await, svctm, %util )?

I'm using Redhat Linux 6.5 and would like to see the disk latencies for the used disks. Using iostat I get the columns await and svctm ( including %util ). But according to the man page of iostat ...
Blockdump's user avatar
1 vote
0 answers
391 views

iostat ( column svctm is not trusted any more ) what to use instead?

I'm running a Linux Server with "Oracle Linux Server release 6.5" which is pretty much the same as RedHat Version. I need to determine the latency on my disk devices. The man page of the iostat ...
Blockdump's user avatar
2 votes
0 answers
341 views

Trying to understand iostat for simple sequential read case

I'm looking at the disk I/O performance of a web hosting VPS (virtual server) and I'd like help in understanding the figures that 'iostat' is giving me. This is my very simple sequential read of the ...
Brad's user avatar
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1 vote
0 answers
1k views

How can I get read/write instant speed of a Hard Drive using /proc/diskstats data?

I know that the proc/diskstats file presents these data columns: 1 - major number 2 - minor mumber 3 - device name 4 - reads completed successfully 5 - reads merged 6 - sectors read 7 - time spent ...
Gustavo Portela's user avatar
0 votes
0 answers
132 views

Software raid problem

We have a software raid on our server and we have a problem with disk performances. From time to time disk i/o freezes. During those periods iostat shows that one disk is faster than another. Both ...
Marian's user avatar
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3 votes
2 answers
2k views

Why doesn't my IOstat change its output at all?

My IOstat doesn't change...at all. It'll show a change in blocks being read and written, but it doesn't change at all when it comes to blocks/kB/MB read and written. When the server sits idle...it ...
Sqenix's user avatar
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2 votes
1 answer
3k views

How can I find the CPU resource utilization of a process and all its children [duplicate]

If I have a process that spawns child processes, is there a good way to get a single number representing the combined CPU use of that process and its children? i.e is there a simple shell command ...
Travis Bear's user avatar
2 votes
2 answers
686 views

Current disk load

I'm using iostat to get the current disk load each second with iostat -dx 1 (specially, %util column). However, I'd like to put this in a bash script and control the interval with the watch command ...
Jay's user avatar
  • 257
1 vote
1 answer
1k views

iostat error counters on Solaris

In a Solaris system i use iostat -E and kstat to identify faulted disks. My problem is that I don't know if the problem is on disk, on controller, on bus or on the filesystem layer (ZFS). The key is ...
MrDan's user avatar
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3 votes
1 answer
6k views

Difference between 'sar' and 'iostat' commands

With sar and iowait, we can get CPU time utilization. But, when I executed both commands, I could see significant differences in their outputs. > iostat && sar 1 1 Linux 2.6.32-042stab090....
Mandar Shinde's user avatar
3 votes
1 answer
3k views

Understanding iostat with Linux software RAID

I'm trying to understand what I see in iostat, specifically the differences between the output for md and sd devices. I have a couple of quite large Centos Linux servers, each with E3-1230 CPU, 16 GB ...
Dokbua's user avatar
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