RAID Capacity Calculator

RAID4 Capacity Calculation:
Total usable storage capacity (TB):	1.00 ^*
RAID type:	RAID 4 (stripe set with parity and dedicated parity disk)
Number of RAID groups:	1
Number of drives per RAID group:	3
Total number of drives:	3
Drive capacity (GB):	500
Capacity of a single RAID group (GB):	1000
Space efficiency:	0.6667 (66.67%)
Fault tolerance:	1 disk drive per RAID group
IO penalty (read):	1/1 (one RAID IO per each host IO)
IO penalty (write):	4/1 (4 RAID IOs per each host IO)
Minimum number of drives per RAID 4 group:	2 (in NetApp implementation)
Single drive cost:
Cost per TB usable:
Total cost:

RAID 4 is not commonly used due to its write performance shortcomings. Since all parity information is written to one drive, write performance of a RAID 4 group is equivalent to performance of a single drive.

NetApp is probably the only major storage vendor that has implemented RAID 4 in its storage appliances. RAID 4 performance shortcomings are mitigated by the NetApp proprietary Write Anywhere File Layout (WAFL). WAFL never overwrites existing disk blocks and stores new data using available free space. In addition, WAFL optimizes disk write operations by caching and aggregating incoming write requests in NVRAM first, and then writing data to disks in full stripes.

^* Storage reserved for WAFL operations reduces usable capacity provided by the underlying RAID group(s). For more details see NetApp Usable Space Calculator.

Note: 1 TB = 1000 GB and 1 TiB = 1024 GiB

About:

This calculator computes RAID capacity characteristics for the most commonly used RAID types.

Provide the following parameters: the RAID type, the disk capacity in GB, the number of disks drives per RAID group and the number of RAID groups (if your storage system consists of more than one RAID group of the same configuration).
To perform calculation click Submit.

Optionally, enter the single disk cost to calculate the total storage cost and the cost per TB of usable capacity.

Supported RAID levels are:

RAID 0 (block-level striping without parity or mirroring);
RAID 1 (mirroring without parity or striping);
RAID 1E (mirroring with striping);
3-Way Mirror or Triple Mirror (mirroring without parity or striping);
RAID 3 (byte-level striping with a dedicated parity disk);
RAID 4 (block-level striping with a dedicated parity disk);
RAID 5 (block-level striping with distributed parity);
RAID 5E (RAID 5 Enhanced) and RAID 5EE (RAID 5E Enhanced) (block-level striping with distributed parity and integrated active distributed hot-spare);
RAID 6 (block-level striping with double distributed parity);
RAID 10 (1+0) (striped mirrors - a combination of multiple RAID 1 groups with RAID 0);
RAID 50 (combination of multiple RAID 5 groups with RAID 0);
RAID 60 (combination of multiple RAID 6 groups with RAID 0);
RAID-DP (stripe set with double parity and two dedicated parity disks);
RAID-TEC (triple erasure encoding);
RAID-Z1 (single parity with variable stripe width);
RAID-Z2 (double parity with variable stripe width);
RAID-Z3 (triple parity with variable stripe width).