The iowait tag has no wiki summary.
1
vote
1answer
44 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
47 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: ...
1
vote
1answer
105 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/ ...
0
votes
0answers
118 views
Mysql Innodb native AIO flag causes high apparent iowait on virtualised host
There is a mysql config setting for InnoDB
innodb_use_native_aio = 0
This is documented here:
http://dev.mysql.com/doc/refman/5.5/en/innodb-parameters.html#sysvar_innodb_use_native_aio
It is ...
1
vote
0answers
159 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
272 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 - ...
0
votes
1answer
161 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
135 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
292 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
329 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
768 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
197 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
221 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 ...
2
votes
4answers
2k 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
377 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 ...
2
votes
1answer
204 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
278 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
2k 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
483 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
330 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) ...
0
votes
2answers
1k 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
593 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
459 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 ...
3
votes
4answers
11k 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
298 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
98 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
1k 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
6k 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 ...
2
votes
2answers
7k 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 ...
3
votes
2answers
3k 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 ...
30
votes
5answers
16k 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
2k 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, ...
