Knowledgebase: RAID Management
Why the capacity is smaller than it should be?
Posted by - NA -, Last modified by on 11 January 2011 17:56
Basically, please refer to the following links,
Based on these knowledge's, we acknowledges that the data capacity might be smaller than what you think. For example, a RAID-5 with 5 * 2TB disks, in ideal it should be a 8TB RAID-5.  While we calculates in terms of binary, it should be 8*1000*1000*1000/1024/1024/1024 = 7.45TB

This would be the ideal capacity of a RAID-5 with 5 * 2TB disks. While you create a RAID-5, the unit(*1) might use 95% capacity for data storage, and Thecus NAS might need keep some space for system and inode (http://en.wikipedia.org/wiki/Inode)  fore file system, that is why you see the capacity is smaller than 7.45TB.

About the capacity,

1. N disks 2TB JBOD = N*2 TB  without redundancy
2. N disks 2TB RAID0 = N*2 TB  without redundancy
3. N disks 2TB RAID1 = 2 TB
4. N disks 2TB RAID5 = (N-1)*2 TB, at least 3 disks.
5. N disks 2TB RAID6 = (N-2)*2 TB, at least 4 disks.
6. N disks 2TB RAID10 = (N/2) * 2TB, at least 4 disks.
7. N disks 2TB RAID50 = (N/2 - 1)*2TB * 2 = (N-2) * 2TB, at least 6 disks.
8. N disks 2TB RAID60 = (N/2 - 2)*2TB * 2 = (N-4) * 2TB, at least 8 disks.


*1. N4100PRO or above, please check the specification.
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