Hi,
do you have the rotational flag set on the nbd block device? If not, try
setting that to enable the IO request elevator to merge requests.
--
Paul
On Wed, Feb 12, 2014 at 10:49 PM, 刘海锋 <[email protected]> wrote:
>
>
> Iostat as below:
>
>
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm
> %util
> sda 0.00 564.67 0.00 53.33 0.00 4944.00 92.70 0.03 0.47 0.15 0.80
> nb0 0.00 0.00 0.00 8765.33 0.00 70122.67 8.00 144.72 16.48 0.11 100.00
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm
> %util
> sda 0.00 585.33 0.00 51.00 0.00 5090.67 99.82 0.02 0.48 0.16 0.80
> nb0 0.00 0.00 0.00 8716.67 0.00 69733.33 8.00 145.14 16.64 0.11 99.97
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm
> %util
> sda 0.00 561.33 0.00 50.67 0.00 4896.00 96.63 0.01 0.24 0.09 0.47
> nb0 0.00 0.00 0.00 8815.00 0.00 70520.00 8.00 145.25 16.51 0.11 100.00
>
>
>
>
>
> In contrast to Centos64, the official kernel 2.6.32 doesn’t have this
> problem �C it merges io requests into 100+ kB.
>
>
>
>
>
> *发件人:* 刘海锋 [mailto:[email protected]]
> *发送时间:* 2014年2月13日 11:44
> *收件人:* '[email protected]'
> *主题:* NBD io request size is always 4KB on Centos6.4
>
>
>
>
>
> Dear nbd maintainers/users,
>
>
>
> Recently we found an annoying case: iostat shows the read/write IO
> requests from nbd are very small (always 4kB exactly without any merges) on
> Centos64.
>
>
>
> And we tried tuning various kernel parameters but failed to solve it. Any
> suggestions?
>
>
>
> Thank you all.
>
> --haifeng
>
>
>
>
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