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Old 01-28-2011, 02:33 PM   #1
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Default Raid5?

i've been doing CompTIA and MS qualifications recently, and one of my areas of 'interest' if you will is hardware/software RAID.

now, RAID5 is striping with 'parity' and uses 3 or more disks, so that if one dies the other two can carry on being striped. In this setup is the total of the RAID5 volume still the total value of all 3+ disks? I've got a question regarding this that has baffled me for a bit, since i've only looked in theory at RAID5.

Say, you have 3x1TB disks, totalling 3TB.

[1024GB] - [1024GB] - [1024GB]

Striped, this would theoretically show up as

[3072GB]

now, if you had 3000GB of data on this 3072GB disk, and one of the disks broke:

[1024GB] - [1024GB] - [XXXXX]

you now have only 2048GB of storage since 1024 of it has broken an is now disregarded. How does 3000GB of data stay intact on a 2048GB stripe?


EDIT: unless, it only uses the third disk when one breaks? so your actual total would only be 2048GB to begin with?
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Old 01-28-2011, 02:56 PM   #2
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Default Re: Raid5?

Raid 5 has overhead: The storage capacity of a RAID 5 array is the number of drives - 1 / number of drives

So 3 drives minus 1 = 2 drives, 2 divided by 3 = 2 drives storage capacity (( 3-1) / 3) = 2

Three 1024GB drives in RAID 5 configuration would yield 2048GB of storage.

[Edit]

Note: Any one drive can fail without data loss because the parity information is distributed among the drives with the data. Of course, performance drops until the failed drive is replaced and the data is restored by the array.

[End edit]
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Old 01-28-2011, 02:57 PM   #3
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Default Re: Raid5?

i see, thanks for clearing that up ^_^
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Old 01-28-2011, 03:54 PM   #4
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Default Re: Raid5?

for raid5 if you have 3 1tb drives the raid will show up as 2tb (As said above)

But you can also configure the raid 5 to have an online spare, which means 2 of the drives will be on standby
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