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Questions tagged [iowait]

72 questions
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votes
4 answers

MySQL on VM, High IO Wait but low TPS

We are trying to figure out a strange situation on our MySQL installation on VM. We are on Mysql 5.7 and RHEL 7 with XFS. We are observing when we run a few select queries the IOWait races up to 40-50% while we see the Disk Read speeds dont cross…
Kiran Thummalapalli
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2 answers

Drawbacks of setting a high I/O timeout?

I'm working on several Linux VMs whose partitions are mounted on a NetApp NAS. This NAS periodically experiences a very high iowait which causes the VM disks to switch to read-only mode, crash, or be corrupted. On the VMware KB it is suggested to…
dr_
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1 answer

CentOS6 and long Wait IO time on jbd2/dm-0-8

Linux box running CentOS 6.5 and 2.6.32-431.3.1.el6.i686 kernel recently got CPU spikes up to 99% causing by Wait IO. Executing while true; do date; ps auxf | awk '{if($8=="D") print $0;}'; sleep 1; done gives me on those CPU spikes: root 300…
JackTheKnife
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3 answers

Is slow IO on my cloud server causing my slow server restart issues?

I'm running two servers on Rackspace cloud one for the web app and one for the db and redis instances. The web server has 1Gb of ram and single core. Nginx sits in front of unicorn which is running 2 workers. I also have a sidekiq instance running.…
toxaq
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1 answer

How to combine different pidstat outputs (CPU, I/O, Disk Usage)

I would like to use pidstat to get both -u, -r and -d flags. Is there a way to do so? The idea, is to get both CPU, I/O and disk usage. Cheers Ps. Combining the flags as -urd doesn't work in Ubuntu 11.04
Emanuele
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3 answers

Apache 2 handling requests very slow after Restart

We have a GPS device socket handling server using NodeJS which sends the received HTTPS request to Apache installed server and saving the data into MySQL Database. When we restart NodeJS or Apache installed server, Request Handling rate of the…
jAddict
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2 answers

Would software RAID0'ing SSDs help or hinder maximization of useful CPU work throughput?

My question is in the title... here is some background: [OS is Linux.] [UPDATE: The contents of this RAID0 is redundant (sync'd from SCM). I am not worried about the increased risk of data loss.] [UPDATE 2: Practically, I'm likely splitting hairs…
Cognitive Hazard
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1 answer

Read IO Wait Increase

While troubleshooting a performance issue on a Debian Linux box running ext3 on software RAID 1 I redirected the output of a process writing useless temporary log files to /dev/null (ln -s /dev/null/ foo) which has reduced write operations by around…
Fat Finger
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1 answer

Debugging I/O issues on a linux server

What are some ways to debug I/O issues on a linux server? I've been using: # nohup top -b -d 10 > /var/log/top.log & # nohup iotop -b -d 5 -o -t > /var/log/iotop.log & PS: hardware is clean, new and fine. SWAP is not being used at all and I see a…
Tiffany Walker
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1 answer

no disk io but iowait very high

there is no disk io going results of iotop Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO< COMMAND 1 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % init [3] 1930 be/4…
Dan
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1 answer

IOwait peaks blocks the whole server for 1-3 minutes

On my Debian VPS, I am getting peaks of IO wait, which blocks my server for a few minutes. On the screenshot, you can see the Idle (green) which suddenly drops for IOwait (pink), which eventually blocks even the logging process (white stripe). There…
Vojtěch
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1 answer

IO-intensive processes hang with iowait, but no activity going on

I have a bunch of IO-intensive jobs, and to boost performance, I just installed two SSDs in a compute server, one as a scratch file system, one as swap. After running for some time, all my processes hang in "D" state, consume no CPU, and the system…
Ketil
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3 answers

MySQL on ubuntu very high IOWAIT

Can anyone advice what is going on with my setup. I have mysql server on ubuntu which periodically produce very high iowait. for long time up to 10-20 minutes. During this time system and database almost not available. Sit that using this database…
user330026
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What iowait values are ok?

I am trying to find the bottleneck of a server running a fairly busy php/mysql site. My first culprit was io but iostat shows that on average iowait consumes only %3.60 of cpu time. here is the complete result of issuing iostat: avg-cpu: %user …
alfish
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RHEL8: Does NFS I/O count as part of "%iowait" calculations?

Customer telling us that they see high %iowait in top and iostat output on a busy RHEL8 NFS client. iostat man page clearly says that iowait is related to % of time kernel is waiting on "disk" I/O Question - does NFS I/O count as "disk" I/O in…
arainchi
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