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MonsterMMORPG
Asked: 2021-05-20 07:02:56 +0800 CST

Raid 1 default disk capacity is lesser than the disk sizes. Any ideas? Intel Raid Storage Technology - Raid from Bios

  • 772

Here the screenshots I think they explains everything

The disks are advertised as 1 TB and the real size of the disks are 931.5 GB

I have installed windows server without raid setup for experimentation. Both disks are fully working with no non-useable sectors and all 931 GB is available to use.

enter image description here

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Edit I have found this link

https://support.lenovo.com/tr/en/solutions/ht507601-intelr-rapid-storage-technology-enterprises-default-volume-size-is-not-maximum-size-lenovo-thinkserver

I also see 95% array allocation after deleting raid and trying to compose again

enter image description here

bios raid ssd intel raid1

5 Answers

  1. Best Answer

    This could sound weird, yes,

    But some RAID systems could do one of the followings or both:

    • change block size
    • save some space (tough your case looks pretty much) for themselves metadata

    in this case, it is better to have a look at the Intel's Rapid Storage Documentation

    • 2

  2. You are confusing Gigabytes with Gigibytes. Samsung 850 Evo's are advertised as 1 TB SSDs. Not 960GB. 1TB under the marketing blanket is actually 931.323 Gibibyte.

    Marketing departments like to round everything up, as it seems as more storage. Just use a quick gibibyte to gigabyte converter to see that 1000 Gigabytes is actually 931.323 gibibytes.

    Your raid controller sees everything in gibibytes not in gigabytes.

    • 2

  3. Same question as in your other post.

    https://superuser.com/questions/1650229/raid-1-default-disk-capacity-is-lesser-than-the-disk-sizes-any-ideas-intel-rai

    Since I don't want to Copy-Paste my answer and also link others.

    • 0

  4. Hard disk drive manufacturers market the drives in terms of decimal capacity (decimal numbering system). In decimal notation, one megabyte (MB) equals 1,000,000 bytes, one gigabyte (GB) equals 1,000,000,000, and one terabyte (TB) equals 1,000,000,000,000 bytes.

    Programs such as FDISK, the system BIOS, Windows, and earlier versions of the Mac operating system use the binary (base of 2) numbering system. In the binary numbering system, one megabyte equals 1,048,576 bytes, one gigabyte equals 1,073,741,824 bytes, and one terabyte equals 1,099,511,627,776 bytes.

    Capacity calculation formula

    Decimal capacity / 1,048,576 = MB capacity in binary Decimal capacity / 1,073,741,824 = GB capacity in binary Decimal capacity / 1,099,511,627,776 = TB capacity in binary

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  5. The default size of 884.9GB is exactly 95% of the smallest disk, which is 931.5GB. You can manually change this value to the full 931.5GB if you wish to do so.

    This feature is documented at https://www.intel.com/content/dam/support/us/en/documents/ssdc/ssd-software/RSTe_NVMeProduct%20Spec.pdf. Its purpose is to protect against NVMe of different sizes. Your current disks are 931.5GB but the next one you buy (if it is a different vendor) could be 931.4GB. A smaller disk cannot be used to replace a bigger one in a RAID1 array. Rounding down the size to 95% gives you a bit of leeway there, but you are free to make it use 100% the space.

    To quote the relevant section 2.6.3 of the document above:

    Disk Coercion

    The Intel RSTe NVMe will provide support for Disk Coercion. When a RAID volume is created, this feature will analyze the physical disks and will automatically adjust (round down) the capacity of the disk(s) to 95% of the smallest physical disk. This allows for the variances in the physical disk capacities from different vendors.

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