Promise Atlas S8+ Volume size
Introduction:
When a user adds a 4TB disk to their computer and looks at the space available, many are surprised that they see 3.8TB of usable space in their file manager, the disk appears to be smaller than what they had purchased. This is one oddity in the computer field, when hard disk manufacturers sell drives, they do not use digital sizing, they size by SI (metric) units.
A kilobyte is 210 bytes, which is 1024 bytes. Using metric units, a kilo is 1000. Here we see a difference of 24 bytes. But as the disk size increases, the difference gets larger, for a 1TB drive, the OS will see 931MB, and for a 4TB drive, the OS will see 3.8TB.
With disk arrays, especially RAID arrays with redundancy, the disk space seen can be much less than the sum of the sizes of the individual disks.
Atlas S8+ usable Volume size
14TB Disks
For the first example, the Atlas S8+ will be loaded with (8) 14TB disks. This is a raw capacity of 112TB.
As you can see, a 14TB disk is seen by the Atlas S8+ (or any computer) as being about 13TB, the larger the disk, the greater the difference between metric and binary.
After a quick setup, which creates a RAID5 disk pool, the Pool size is 85700.53GB.
The Volume size is 83.69TB
They are the same however as 85700GB = 83.69TB.
The total disk capacity is 13039GB * 7 = 91273GB = 89.13TB. But our Volume size is 83.69TB. The difference of 5.4TB is taken up by filesystem overhead.
4TB Disks
For the second example, the Atlas S8+ will be loaded with (8) 4TB disks. This is a raw capacity of 32TB.
With a 4TB disk we see the following…
The 4TB disk has a usable space of 3726GB.
After a quick setup, which creates a RAID5 disk pool, the Pool capacity is 24394.15GB
The Volume size is 23.82 TB…
But as before, 24394.15GB = 23.82TB.
The total disk capacity is 3726GB * 7 = 26082GB = 25.47TB. But our Volume size is 23.82TB. The difference of 1.65TB is taken up by filesystem overhead.
