For hard disk drives, which use rotating media, speed is measured in revolutions per minute (RPM). Faster disks provide more disk input/output operations per second (IOPS) and faster response time.
It is best to use disks of the same speed in an aggregate.
Data ONTAP supports the following rotational speeds for disks:
Solid-state disks, or SSDs, are flash memory-based devices and therefore the concept of rotational speed does not apply to them. SSDs provide more IOPS and faster response times than rotating media.
For more information about supported disk speeds, see the Hardware Universe at hwu.netapp.com.