Data storage values

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This topic describes the units of measurement used to express data storage values in the online IBM Storage Archive Library Edition documentation.

Decimal units (base-10), such as kB, MB, GB, and TB, are commonly used to express data storage values. These values, however, are more accurately expressed using binary units (base-2), such as KiB, MiB, GiB, and TiB. At the kilobyte level, the difference between decimal and binary units of measurement is relatively small (2.4%). This difference grows as data storage values increase. When values reach terabyte levels, the difference between decimal and binary units approaches 10%.

To avoid confusion, the online IBM Storage Archive Library Edition product documentation represents data storage using both decimal and binary units. Data storage values are displayed using the following format:
#### decimal unit (binary unit)
For example, a value of 512 terabytes is displayed: 
512 TB (465.6 TiB)

By default, CLI (eeadm command) displays the storage capacity in decimal, and --unit option allows to show the capacity in binary.

Table 1 compares the names (prefixes), symbols, and values of decimal and binary units. Table 2 shows the increasing percentage of difference between decimal and binary units.
Table 1. Comparison of decimal and binary units and values
Decimal Binary
Name Symbol Value (base-10) Name Symbol Value (base-2)
kilo k 103 kibi Ki 210
mega M 106 mebi Mi 220
giga G 109 gibi Gi 230
tera T 1012 tebi Ti 240
peta P 1015 pebi Pi 250
exa E 1018 exbi Ei 260
Table 2. Percentage difference between decimal and binary units
Decimal value Binary value Percentage difference
100 kilobytes (kB) 97.65 kibibytes (KiB) 2.35%
100 megabytes (MB) 95.36 mebibytes (MiB) 4.64%
100 gigabytes (GB) 93.13 gibibytes (GiB) 6.87%
100 terabytes (TB) 90.94 tebibytes (TiB) 9.06%
100 petabytes (PB) 88.81 pebibytes (PiB) 11.19%
100 exabytes (EB) 86.73 exbibytes (EiB) 13.27%