[CentOS] Very slow disk I/O

[Jatin Davey]

On 2/3/2015 10:00 AM, John R Pierce wrote:
> 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.
>
>
>
>
So , You dont think that any configuration changes like increasing the 
number of volumes or anything else will help in reducing the I/O wait time ?

Thanks
Jatin