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Calculating space for parity in RAID-5

Brett Cooper offers advice to a reader who asked: "What are the calculations for RAID-5 in regards to the amount of space parity will consume? For instance, if I have a RAID-5 with 10 146 GB drives, what is the percent factor of space used for parity?"

What are the calculations for RAID-5 in regards to the amount of space parity will consume? For instance, if I have a RAID-5 with 10 146 GB drives, what is the percent factor of space used for parity?

I just got asked the same question a few weeks ago. In answer to your specific question, 10[x] 146 GB drives in a RAID-5 configuration would provide 1.316 TB of useable space. The way that I figured this out is using a RAID calculator from ibeast that can be found at: http://www.ibeast.com/content/tools/RaidCalc/RaidCalc.asp

Also, a fellow SearchStorage.com expert, Stephen Foskett answered a similar question and provided a formula for calculating disk space on RAID-5 sets: http://searchstorage.techtarget.com/ateQuestionNResponse/0,289625,sid5_cid637415_tax297924,00.html

The space calculation shows that the parity stripe would consume approximately 10% of the overall storage space, or 146 GB of disk space.

This was first published in January 2005

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