Raid Calculations

Electronics, Linux, SysAdmin, Technical
The only redundant storage technique available that uses 3 drives is called RAID-5. This storage array allows one drive in your system to fail, while still retaining all of your data. The basic math behind Raid-5 is (# of Drives * GB per drive) – ( GB per one Drive) Raid can only use the maximum disk space for the smallest drive you have. In your case, a typical 3TB drive is 2794 GB. This plugged into the equation gives: (3 * 2794) – (2794) = 5588 GB of usable storage. (5.58 TB) Your 5TB drive will essentially waste it's extra 2TB and be used as a 3TB drive.
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A little “Storage Spaces” tidbit

Electronics, SysAdmin, Technical
Although Storage Spaces in Windows 8, 8.1 and 10 allow mixing drives of different sizes, it is recommended to use drives that have similar capacity to avoid wasting disk space. For example, if you put one 300 GB disk and one 750 GB disk into a two-way mirror, you'll get a Storage Space (virtual disk) of 525 GB in size. The calculation is (300+750)/2 – to provide fault tolerance, only half of total disk space is available while using two-way mirror. The other half is used for data redundancy in case one of the drives goes offline for some reason. But mirroring means that all member drives contain exactly the same data. That's why the real usable space in this example maxes out at 300 GB (the smaller physical disk…
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