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If we consider, hypothetically, that a server farm is being designed to have 100TB of storage using solid state drives (SSD), each with 250GB each.

My question is how many SSD are needed to ensure redundancy by:

i) RAID 1

ii) RAID 3

iii) RAID 5

What and why is the best choice?

Note that this is an hypothetically question in order to better understand RAID.

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  • 4
    Please hire someone to help you out with this.
    – EEAA
    Jul 22, 2015 at 18:11
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    @FranciscoMariaCalisto - no problem, it's a badly worded and researched question, I've answered you but it's more than you deserve - please don't post again until you can meet the requirements laid out very clearly in the help pages we ask new users to read before posting.
    – Chopper3
    Jul 22, 2015 at 18:15
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    Because if you're asking this type of question, you need more assistance and guidance than an internet QA site can reasonable offer.
    – EEAA
    Jul 22, 2015 at 18:16
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    @FranciscoMariaCalisto To add weight to EEAA's comment, you need someone to help you who knows that R3 hasn't been used since the early '90's and R5 hasn't been recommended this decade. This is either homework, which isn't allowed on this site, or you're out of your depth and need help. Sorry if you feel we're being harsh but as we make clear when you sign up this site is for professional sysadmin, not learners, not home users, not tinkerers.
    – Chopper3
    Jul 22, 2015 at 18:23
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    possible duplicate of What are the different widely used RAID levels and when should I consider them?
    – HBruijn
    Jul 22, 2015 at 19:26

2 Answers 2

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For RAID 1 you will get half of the total data size of all drives so you would need 800 drives to get 100TB

RAID 5 will give you all the data minus 1 drive so 401 would be needed.

I believe RAID 3 would require the same 401 drives

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NONE of those options are valid, you can do it in two ways;

  • RAID 10 - you'll need 80 SSDs of that size to give you 100TB, though that doesn't include the typical overhead you'd see so I'd personally go for 90-100.

  • RAID 60 - you'll need 44 SSDs of that size to give you 100TB, this is via 2 x 20+2 R6 arrays, again I'd actually increase this to 50-60 to deal with overhead.

You'd also want at least two disks to act as hot-standby.

This is actually really easy to do by the way, just make sure you get a good disk controller and matching shelves.

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    Shouldn't that be 800 for RAID 10 and 404+ for RAID 60?
    – william
    Jul 22, 2015 at 18:51
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    Erm...good point, well made :) see his stupid question made me drop a zero!
    – Chopper3
    Jul 22, 2015 at 19:23
  • Thank you again @Chopper3 you are lovely. I will learn a lot with your words.
    – Francisco Maria Calisto
    Jul 22, 2015 at 19:36

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