Raw Disk Space Calculation w/ HP 3PAR in mind

Hopefully this information won’t be redundant but sometimes the propagation of sizing a storage solution should go beyond the calculation given by a tool.

When calculating the space for CPGs and VVs in 3PAR the measurement the unit used is TiB (Tebibyte) / GiB (Gibibyte) / MiB(Mebibyte) where:

  • Each TiB = 1.099511627776 TB.
  •  Each GiB = 1.073741824 GB.
  • Each MiB = 1.048576 MB.

You can use this website http://www.unitjuggler.com/convert-memory-from-TiB-to-TB.html for conversion, till now I presume this is know if you have a keen eye on noticing the measurement unit.

On the other hand please take into consideration that the partition on Windows for example when initialized even though for example it’s a 16TiB (17.55TB) the usable disk space will be 15.9TB, why? After doing some research I found out that to the hard disk manufacturers, one KB is 1000 bytes, one MB is 1000 KB, and one GB is 1000 MB.

So if a hard disk is advertised as 1TB, it contains [1000 * (1000 * 1000 * 1000) = 1000,000,000,000 bytes of space]. The hard disk manufacturer thus advertises the disk as a 1TB hard disk so to get the exact number of available space for Windows we have to follow the following calculation because on the Windows OS a 1TB is 1024GB, as such we have to : [1000,000,000,000 / (1024 * 1024 * 1024) = ~931GB usable disk space].

Hopefully this would be informative to someone.


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