[CentOS] Very slow disk I/O

Tue Feb 3 04:30:28 UTC 2015
John R Pierce <pierce at hogranch.com>

On 2/2/2015 8:11 PM, Jatin Davey wrote:
> disk 252:1 | 0-0-0 | 9XG7TNQVST91000640NS CC03 | Online, Spun Up
> disk 252:2 | 0-0-1 | 9XG4M4X3ST91000640NS CC03 | Online, Spun Up
> disk 252:3 | 0-1-1 | 9XG4LY7JST91000640NS CC03 | Online, Spun Up
> disk 252:4 | 0-1-0 | 9XG51233ST91000640NS CC03 | Online, Spun Up
> End of Output **************************
>
> Let me know if i need to change or configure anything else to make the 
> I/O a bit faster than what it currently does. I cannot go in for using 
> SSD's due to budget constraints. Need to make the best use of the SATA 
> disks that i have currently. 

so, you have 2x2 ST91000640NS
http://www.seagate.com/products/enterprise-servers-storage/nearline-storage/enterprise-capacity-2-5-hdd/

those are "Nearline" disks, 7200RPM.  They are intended for bulk 
secondary storage, archives, backups and such.

you said you have a number of virtual machines all attempting to access 
this raid10 at once?  I'm not surprised that it is slow. You're probably 
limited by random IO/second, that raid likely does around 250 random 
operations/second.   share that between 6-7 virtual systems and if they 
are all doing disk IO, they are going to slow down each other.




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