Calculating available disk space in a RAID-5 set

Five 36 GB drives in a RAID-5 configuration yields 144 GB of useable space. I figured this out using a RAID calculator from ibeast that can be found at http://www.ibeast.com/content/tools/RaidCalc/RaidCalc.asp

In addition to providing the simple RAID calculations, the tool also provides information on the various RAID configurations. For RAID-5, the tool provides:

RAID level 5 data striping with distributed parity definition
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Data is striped across a group of disk drives with distributed parity. Parity information is written to a different disk in the array for each stripe.

Redundancy
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Parity is distributed across the disks in the array. Data is regenerated in the event of a drive failure.

Performance
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High performance in small record, multiprocessing environments because there is no contention for the parity disk and read and write operations can be overlapped. No write bottlenecks as with RAID-4.

Drawbacks
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Distributed parity causes overhead on write operations. There is also overhead created when data is changed, because parity information must be located and then recalculated.