SDA, SDB, SDC, SDD etc..

Hi,
I have HiMedia Q10 Pro and I have a problem.
I’m using Kodi (v16.1 Jarvis) on the device.
I ‘ve attached 3 external disks to the device (with an internal HDD too).
Every time I start the machine and startup Kodi, the letters assigned to these attached USB drive’s change : SDA, SDB, SDC, SDE etc..)
Is it a problem from OS (Linux), or from Android version (mine is Android 5.1), or firmware (mine is 1.0.8-FUTEKO-EN. HMD-1.0.8 2016-10-12.193826)
If you help by chance, I will be very happy.
Thanks.