[CentOS] Very slow disk I/O

Thu Jan 29 12:55:05 UTC 2015
Jatin Davey <jashokda at cisco.com>

On 1/29/2015 4:50 AM, Gordon Messmer wrote:
> On 01/28/2015 04:32 AM, Jatin Davey wrote:
>> Could someone point me on how to improve the disk I/O on my server and
>> reduce the wait time on I/O.
> Start by identifying your disk and controller.  Assuming that this is 
> a single SATA disk:
> # smartctl -a /dev/sda | egrep 'Model:|Rate:|SATA Version'
[root at localhost images]# smartctl -a /dev/sda | egrep 'Model:|Rate:|SATA 
[root at localhost images]#

> # lspci | grep SATA
[root at localhost images]# lspci | grep SATA
00:11.4 SATA controller: Intel Corporation Wellsburg sSATA Controller 
[AHCI mode] (rev 05)
00:1f.2 SATA controller: Intel Corporation Wellsburg 6-Port SATA 
Controller [AHCI mode] (rev 05)
> Next install and run iotop.  If there's something on your system 
> that's particularly active and unnecessary, disable it.
> If everything contending for your disk *is* necessary, then you may 
> need to take steps to improve disk performance.  There are a number of 
> possibilities.
> 1: Use an SSD instead of a disk.
> 2: Use an SSD in addition to a disk.  If a purely SSD storage system 
> is too expensive, you might choose to use an SSD for one or more 
> filesytems that you can mount where the high volume IO is occurring, 
> and continue to use the disk for filesystems that need more data 
> capacity and fewer IOPS.
Thanks for these inputs. I will surely take it up with my team to see if 
we can incorporate new hardware for our product.
> 3: Use a fast RAID array.  A RAID1 array can provide better read 
> performance than a single disk.  For higher write volumes, use RAID10 
> on four or more disks.  Avoid RAID 5 or 6, as they'll be slower than a 
> single disk.
We are using RAID 10 in our server with 4 disks.
> 4: Replace poorly supported hardware.  It might be that your SATA 
> controller isn't well supported, and performs badly as a result. I 
> used to have a desktop system with NVidia motherboard chipset. Its 
> SATA controller was garbage.  Performance with the same disk was 
> noticeably better with a cheap PCI-E SATA controller.
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Hi Gordon

Please see my responses inline to your questions.
Appreciate your inputs in this direction.