Process jbd2/vda1-8 high loading

I am using a $10/month droplet with Ubuntu 14.04. I noticed that a process named “jbd2/vda1-8” pops up from time to time. As soon as it runs, all Apache processes become blocked and my entire server becomes unresponsive.

Some output from “ps auxf” command:

Wed May 27 15:58:10 UTC 2015
root       199  0.0  0.0      0     0 ?        D    May19   6:52  \_ [jbd2/vda1-8]
Wed May 27 15:58:11 UTC 2015
root       199  0.0  0.0      0     0 ?        D    May19   6:52  \_ [jbd2/vda1-8]
www-data 27636  0.0  0.9 406192  9604 ?        D    15:57   0:00  \_ /usr/sbin/apache2 -k start
Wed May 27 15:58:12 UTC 2015
root       199  0.0  0.0      0     0 ?        D    May19   6:52  \_ [jbd2/vda1-8]
www-data 27362  0.1  1.1 405668 11672 ?        D    15:56   0:00  \_ /usr/sbin/apache2 -k start
www-data 27636  0.0  0.9 406192  9604 ?        D    15:57   0:00  \_ /usr/sbin/apache2 -k start
www-data 27685  0.3  1.3 408368 13812 ?        D    15:57   0:00  \_ /usr/sbin/apache2 -k start
www-data 27738  0.2  0.9 405252  9340 ?        D    15:57   0:00  \_ /usr/sbin/apache2 -k start

The “top” command also shows “wa” above 90.

I realized it is something to do with disk journaling. Can it be disabled, or is anything I can do to reduce the load from “jbd2” without affecting my droplet?

Thanks for any advice!