The My Cloud is what it is. The processor is low powered. As such it takes longer for the OS to perform scanning of files one copies to the unit. Depending on the file types one copies to unit it could take some time for the unit to scan the files. During that time other access to the unit may be sluggish or slow down.
There are various threads discussing how to disable certain features and functions (like from the dashboard; remote access, twonky media server, iTunes media server, ftp, etc.) to speed up the My Cloud and turn it into a basic NAS without all the bells and whistles, but disabling those features and functions may disable things like Remote Access and DLNA client access. The two services people normally disable (using SSH) are: wdmcserverd and wdphotodbmergerd. That tends to speed up the unit a bit. Here are a few threads.
http://wdstagingsplit.staged-by-discourse.com/t/is-there-a-way-to-disable-the-content-scan/92802
http://wdstagingsplit.staged-by-discourse.com/t/wdmcserverd-and-wdphotodbmergerd-disable/140441
http://wdstagingsplit.staged-by-discourse.com/t/stripping-mycloud-to-minimum/96014
