[CentOS] Very slow disk I/O

[David Both]

+1

And remember that I/O is more than just disk. The atop monitor gives you 
information like top and htop, but also provides a lot of I/O information as 
well including network. Perhaps your server is the target of a network-based 
DDOS attack which can cause lots of I/O wait time. Also look at top to see what 
numbers are in the si and hi columns. THese stand for software and hardware 
interrupts. If one of those is high you can also narrow it down.

Hope this helps.

On 01/28/2015 07:51 AM, Nicolas Thierry-Mieg wrote:
> On 01/28/2015 01:32 PM, Jatin Davey wrote:
>> Hi Users
>>
>> I am using RHEL 6.5 on my server.
>>
>>  From top command i can see that the processors in my server are
>> spending a lot of time on wait for I/O.
>> I can see high percentage in terms of 30-50% on "wa" time.
>>
>> Here is the df output about the disk space in my system:
>>
>> **********
>> [root at localhost images]# df
>> Filesystem      1K-blocks      Used  Available Use% Mounted on
>> /dev/sda1      1915071844 103227908 1714563936   6% /
>> tmpfs            32931472         0   32931472   0% /dev/shm
>> **********
>>
>> Could someone point me on how to improve the disk I/O on my server and
>> reduce the wait time on I/O.
>
> you could use iotop or vmstat to see what processes are causing the IO.
>
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