Usable and physical disk capacity by disk size

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Usable and physical disk capacity by disk size

You need to understand both the physical and usable capacity of the disks you employ in your storage systems to ensure that your storage architecture conforms to the overall system capacity limits and the size limits of your aggregates.

To maintain compatibility across different brands of disks, Data ONTAP rounds down ("right-sizes") the amount of space available for user data. In addition, the way that capacity measurements are calculated (base 2 or base 10) also impacts sizing information. For these reasons, it is important to use the correct size measurement, depending on the task you want to accomplish.

For calculating overall system capacity, you use the physical capacity of the disk, and count every disk that is owned by the storage system. Note that the physical capacities listed in the table below are only approximations; actual physical disk capacities vary by disk manufacturer. See the technical documentation for your disks for the exact physical disk capacities.

For calculating how many disks you can put into an aggregate before you exceed its maximum size, you use the right-sized, or usable capacity of all data disks in that aggregate. (Parity and dparity disks are not counted against the maximum aggregate size.)

The following table lists the approximate physical and usable capacities for the disk sizes currently supported by Data ONTAP. This same information can be obtained by using the sysconfig -r command (available through the nodeshell) for disks installed in your storage system.

Note: The numbers shown in the table below are in Mebibytes (MiBs). This unit of measure is equivalent to 2 to the 20th power bytes. (MBs, in contrast, are 10 to the sixth power bytes.)

Disk size as described by manufacturer	Physical capacity (approximate)	Usable capacity
100 GB SSD (X441A-R5)	95,396 MiB	95,146 MiB
100GB SSD(X442A-R5)	84,796 MiB	84,574 MiB
300 GB SAS/FC	280,104 MiB	272,000 MiB
450 GB SAS/FC	420,156 MiB	418,000 MiB
500 GB SATA	423,946 MiB	423,111 MiB
600 GB SAS/FC	560,208 MiB	560,000 MiB
1 TB SATA	847,884 MiB	847,555 MiB
2 TB SATA	1,695,702 MiB	1,695,466 MiB
3 TB SATA	2,543,634 MiB	2,538,546 MiB

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