[CentOS] Very slow disk I/O

Wed Jan 28 17:37:23 UTC 2015
John R Pierce <pierce at hogranch.com>

On 1/28/2015 4:32 AM, Jatin Davey wrote:
> 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. 

it appears you have everything on a single file system on a single 2TB 
drive?    I'm going to guess thats a desktop grade SATA disk spinning at 
most at 7200rpm (many are slower, 'green' disks are often 5400rpm).

what sort of workload are you running?    our high disk IO servers, 
doing things like transactional databases, have many 10000rpm or 15000 
rpm drives on a SAS2 raid card with 1GB or 2GB of write-back-cache 
(battery or flash backed).

john r pierce                                      37N 122W
somewhere on the middle of the left coast