Q

Calculating available disk space in a RAID-5 set

Learn how to calculate disk space availability for five 36 GB disks using RAID-5.

I'm trying to find out how to calculate how much disk space will be available from five 36 GB disks using RAID-5. Can you help me out?

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.

This was first published in January 2005

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