How to calculate the estimated time of completion of a RAID Initialization Process

RAID initialization is a disk intensive process. The time required to fully initialize an array is dependent upon the size and speed of each drive, and how the controller’s driver is designed to transfer the data.

It is also heavily dependent on the initialization method – Foreground or Background.

Foreground initialization is recommended in most cases. The controller will make initialization a priority, which will allow the process to progress at a stable rate.

Background initialization allows the operating system to interrupt the process, as other tasks and applications will be given priority. This will increase the length of the Initialization process.

When initializing an array (regardless of method), the controller’s driver will limit transfer size to 64K (per block) to ensure stability.

How to calculate the estimated time of completion ETC):

You can calculate the ETC using the following formula:

xxTB * 1024 * 1024 / XXX / 3600

“xxTB” refers to the size (capacity) of the RAID array. 1024 * 1024 will convert a terabyte value to a megabyte value. “XXX” refers to the maximum speed of the hard drive, as documented by the manufacturer (in MB/s). “3600” refers to the number of seconds per hour.

Important: We should note that this result represents an “ideal time”. In reality, the hard drives will be unable to operate at peak performance for the duration of the initialization process. 

For example, a 10TB RAID 1 array comprised of two drives capable of performing at 245MB/s would take approximately 12 hours to complete (if the drives were able to operate at full speed for the entire process.)

10 * 1024 *1024 / 245 / 3600 = 11.89

In this particular instance, the real-world initialization process took approximately 17 hours to complete. This suggests the drives were able to maintain a transfer rate of 171MB/s (about 70% of the maximum 245MB/s).