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I am from Dell Technical Support -- One of our customers has a Dell System Model T5610 and has installed 2-256GB SSD HDD and 2- 4TB HDD and Configured RAID-0 of 2 Arrays on Intel Based Chipset (ROMB)--- 256GB HDDs is primary for OS installed Ubuntu 14.04 64bit, However when he creates RAID-0 on 2-4TB HDD Using ROMB he sees 100% HDD Capacity in RAID BIOS but in the OS he get to see only 3.2 TB Space,

If he deletes the RAID in RAID BIOS and configure the same in OS level in Ubuntu then he gets 100% Capacity---- Help appreciated, why 100% HDD Capacity is not shown in the OS when the RAID-0 is configured in RAID BIOS (ROMB)

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  • I changed the tags so that more people with expertise can find your question.
    – don.joey
    Sep 26, 2014 at 9:54
  • Hi, can you please be more specific about the hardware ? Dell hardware model ? Intel Chipset ? Southbridge ? Sep 28, 2014 at 16:54
  • The Dell System Model is T5610 and Chipset is Intel and RAID is configured on Intel RAID BIOS CTRL+I
    – MIK
    Sep 29, 2014 at 7:51
  • Can you provide us with more information on the RAID BIOS? version perhaps?
    – Elder Geek
    Oct 2, 2014 at 12:58
  • @MIK Intel has produced numerous chipsets over the years. If you need an answer you need to provide more information.
    – Elder Geek
    Oct 5, 2014 at 14:37

2 Answers 2

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The RAID normally done in BIOS is not full RAID, it is basically "RAID Assistance". It is there to help Windows do RAID as Windows cannot do full software RAID on it's own without some sort of hardware assistance. Linux on the other hand can do software RAID on it's own without any hardware assistance. Trying to use the "RAID Assistance" actually gets in the way and confuses the software RAID. It is generally recommended not to use this "RAID Assistance" when using Linux. (I learnt this one the hard way) As far as I can tell this "RAID Assistance" feature in BIOS's does not bring any performance advantage, it is merely a "compatibility layer" for Windows.

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I think the reason for the 4TB volume only being recognized as less than 4 TB is because storage is sold on base 10 and measured in base 2 and formating takes some space. A base 2 terabyte is 1024 gigabytes, a gigabyte is 1024 megabytes and so fourth. Storage is sold in base 10 teragytes, 1TB=1000GB, 1GB=1000MB, and so fourth.so a 4TB drive is 4 X 10^12 and the os sees that as 3.637978807 * ((2^10)^4) and some of the space will be used for swap and formatting.

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    -1 This question is about RAID and BIOS. Read the first line of the second paragraph.
    – user68186
    Nov 4, 2014 at 18:37

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