Tagged Questions

The tag has no wiki summary.

learn more… | top users | synonyms

0
votes
1answer
31 views

Monitoring/Warning for IOWait

I had a downtime today on my server because of a high IOWait. I could not do mostly anything on the server, I managed only to run top to see the IOWait, but I did not have iotop installed at that ...
0
votes
0answers
46 views

Find cause of unresponsive Ubuntu 14.04 KVM host

I'm hoping someone can point me in the right direction on a very puzzling problem. I've got an older server running Ubuntu 14.04 that serves as a virtual host for some small virtual (KVM) machines. ...
0
votes
1answer
61 views

Apache not serving static content concurrently

When tried to open multiple pages from Codeigniter based custom CMS on different tabs, the first tab loads, while the subsequent tabs wait for the first tab to complete, then sequence follows ...
0
votes
2answers
128 views

High iowait despite small amount of write/read

I'm not sure how to interpret this or the next steps, but why is IOWait so high when I have not written/read much from any devices? Background: I am a developer trying to find why the DB seems to be ...
0
votes
1answer
2k views

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; ...
0
votes
1answer
134 views

Full core of iowait with no actual IO load

I'm having an issue with a box that is "randomly" gaining an entire core worth of iowait -- and as far as I can tell there isn't any IO load to go with it, as illustrated by iostat: avg-cpu: %user ...
0
votes
1answer
153 views

iowait high when uncompress file in EC2 instance (AWS)

this 2 days, i faced very weird problem. When i'm doing uncompress big file, the iowait become very high, more than 70% I do iotop and the result got 3 process with high IO gzip -d filename ...
2
votes
1answer
1k views

Windows “iowait” CPU utilization reporting

Does Windows account for and report "iowait" in the same manner as Linux? That is, processes enter "uninterruptible sleep" and their time spent is subtracted from "CPU free"? If so, which Perfmon ...
0
votes
1answer
226 views

Tracing down High Linux Load - HDD at fault or too many interrupts ? (ksoftirqd Time 437:44.13)

Server Stats: "cat /proc/version" Output Linux version 2.6.18-308.24.1.el5 (mockbuild@builder17.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-52)) #1 SMP Tue Dec 4 17:43:34 EST 2012 ...
4
votes
2answers
405 views

Strange Recurrent Excessive I/O Wait

I know quite well that I/O wait has been discussed multiple times on this site, but all the other topics seem to cover constant I/O latency, while the I/O problem we need to solve on our server occurs ...
0
votes
1answer
645 views

Ubutu/KVM: High iowait on guest nodes, root node fine

Recently one of my boxes has been running quite slowly. It's running Ubuntu 12 LTS and kvm to split the server into several nodes. The box has 2 normal SATA drives using software RAID-1. One of the ...
3
votes
3answers
663 views

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 ...
0
votes
2answers
559 views

High Iowait + High load average on a monitoring server

I've a nagios server which was perfectly working up to a few days ago. I've stopped it and restarted it to increase its RAM, and since then, iowait increased dramatically on the server (more than 20%, ...
2
votes
2answers
150 views

CentOS 5 extremely slow when is running a download

When my server is downloading a file or executing other IO operations the other server functions become extremely slow (almost locked). Even other functions that do not use the network. When a ...
1
vote
0answers
102 views

high linux server load

I have a problem with high server load (load average from 10 to 100+) when there is a lot of web traffic. There are also noticable delays when reading/writing files. Machine is a Apache web server. ...
1
vote
1answer
146 views

Why does md resync cause no iowait?

I've known the defintion of %iowait as Time the CPU spent idling/blocking, because it had to wait on an IO operation to complete. Now take a simple Linux system with an mdraid1 and two disks. ...
1
vote
1answer
67 views

What happened to hard disk

I suspect that with my hard drives is something wrong. iostat -d -x -m root@srv2:~# iostat -d -x -m Linux 2.6.32-5-amd64 (srv2.host.com) 04/23/13 _x86_64_ (2 CPU) Device: ...
2
votes
1answer
195 views

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/ ...
1
vote
0answers
291 views

Copying cause big iowait

I have dedicated server with 3 HDD. System disk, backup disk (same as system disk) and data disk. When I copy lot of data with cp (say, between backup disk and data disk) load average goes sky high. ...
6
votes
4answers
702 views

What would cause IO Wait on a SAN?

I understand IO wait when I see it on a server, it means that the CPU is blocked while I wait for the IO to catch up [source]. I am trying to understand why a SAN stats would show a high IO wait - ...
1
vote
1answer
394 views

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 ...
1
vote
1answer
230 views

How to manage iowait over cifs?

For backup purposes we have Cifs file Server running that contains encrypted containers for backing up the more sensitive data. The container is mounted with cryptsetup and loop as a local filesystem ...
1
vote
1answer
476 views

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 ...
0
votes
2answers
630 views

Why load increase ,ssd iops increase but cpu iowait decrease?

There is a strange thing on my server which has a mysql running on it. The QPS is more than 4000 but TPS is less than 20. The server load is more than 80 and cpu usr is more than 86% but iowait is ...
8
votes
1answer
1k views

high load average, high wait, dmesg raid error messages (debian nfs server)

Debian 6 on HP proliant (2 CPU) with raid (2*1.5T RAID1 + 2*2T RAID1 joined RAID0 to make 3.5T) running mainly nfs & imapd (plus samba for windows share & local www for previewing web pages); ...
1
vote
0answers
268 views

Why does nginx 1.0.0 appear to not use the kernels open file cache on Gentoo? (high iowait)

free -m total used free shared buffers cached Mem: 7996 2043 5952 0 73 140 -/+ buffers/cache: 1830 6165 ...
1
vote
1answer
372 views

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 ...
3
votes
4answers
4k views

What is causing the unusual high load average?

I noticed on Tuesday night of last week, the load average went up sharply and it seemed abnormal since the traffic is small. Usually, the numbers usually average around .40 or lower and my server ...
1
vote
1answer
618 views

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 ...
3
votes
1answer
417 views

How can i view the disk latency of a ZFS pool, or of the disks in it?

I'm using FreeBSD. I would like to write a munin plugin to log it, but i don't understand how to get this data.
1
vote
1answer
619 views

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 ...
5
votes
4answers
4k views

High iowait on Amazon EC2 MySQL instance with EBS volume

We have a MySQL server running on an Amazon EC2 c1.medium instance relying on a single EBS volume using the ext3 filesystem for storage. This MySQL server is queried ~500/ps by several applications ...
2
votes
3answers
783 views

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 ...
2
votes
0answers
420 views

MySQL INSERT … SELECT renders server unresponsive

Solution: Although I haven't found a proper solution yet I'm at least sure that this is purely a disk I/O problem and has nothing to do with MySQL... I have a MySQL server (5.1.54-1ubuntu4-log) ...
1
vote
2answers
3k views

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 ...
0
votes
2answers
789 views

mysqld causing machine to lockup with high iowait

I've inherited a LAMP server running centos, which randomly hangs from time to time despite low web traffic. I've installed Server Density to monitor what's going on, and have found during a hang the ...
0
votes
3answers
555 views

JVM hangs with 100 IO wait on Ubuntu Maverick (AWS EC2 xlarge instance)

Asked this question on on stackoverflow, reposting: Have an xlarge instance in AWS running 9 Tomcats with heaps from 256M to 4G. With Ubuntu 10.04 the box sporadically hangs for a few hours with huge ...
4
votes
4answers
17k views

How to measure IOwait per device?

I have a server, which exports home directories over NFS. They are on software RAID1 (/dev/sdb and /dev/sdc) and the OS is on /dev/sda. I noticed that my %iowait as reported by top and sar are ...
2
votes
2answers
316 views

How do I know if my disks are being hit with too many I/O reads or writes or both?

I know a bit about disk I/O and bottlenecks relating to this especially when relating to databases. How do I really know what the max I/O numbers will be for my disks? What metric might be available ...
0
votes
1answer
113 views

High IOWait executing JBoss 3.2.7

Server Details: Kernel: Linux wiq31 2.4.21-9.ELsmp #1 SMP Thu Jan 8 17:08:56 EST 2004 i686 i686 i386 GNU/Linux CPU: 4 x Intel(R) Xeon(TM) CPU 3.06GHz Memory: 1028520 kB JBoss version: 3.2.7 Every ...
0
votes
3answers
2k views

100% iowait + drive faults in dmesg

I have a server on which resides a fairly visited web app. It has a raid1 of 2 HDDs, 64MB Buffer, 7200 RPM. Today it started throwing out errors like: kernel: ata2.00: exception Emask 0x0 SAct ...
3
votes
2answers
7k views

is CPU actually occupied during iowait (%wa in top) on Linux / EC2?

On an 8-way Amazon EC2 instance (running Linux 2.6.21) with 8 EBS volumes and a lot of disk traffic, we see high %wa in top (30-40%), and high load average (8-9). My understanding is that processes ...
3
votes
2answers
9k views

Finding the root cause of 100% iowait in Linux

I have a system that is a few years old that is running Fedora 7 (I know, it's old too). Now I have PS3 Media Server running (and some other things, like Vmware and Plone) and I noticed that I was ...
5
votes
2answers
4k views

Does iowait include time waiting for network calls?

The proc(5) manpage describes iowait as "time waiting for IO to complete". This was mostly explained in an earlier question. My question is: while waiting in blocking IO, does this include waiting on ...
55
votes
7answers
42k views

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 ...
1
vote
4answers
3k views

Resolving high iowait on Samba server

We've got a centralised file cache which a cluster of web servers use to store "heavyweight" pages. Each webserver uses Samba to mount this shared area. We're getting a lot of iowait on the server, ...