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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

enter image description here

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

Furkan Gözükara
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  • What disks did you select? – Michael Hampton Jun 01 '21 at 19:33
  • this is a normal behavior as they write some extra data, moreover there's a gab between Gigabyte and Gibibyte – djdomi Jun 01 '21 at 19:37
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    Metadata? Not sure, but if you can run Linux (Live distro will do too), you can try creating an array with Intel Metadata from Linux (it will be visible from OpROM) to see which size it will become: https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/rst-linux-paper.pdf – NStorm Jun 01 '21 at 19:39
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    ... or vice versa, create RAID via ROM utility and then explore it with Linux and see what it looks like. And post here `lsblk`, `blkid`, `cat /proc/mdstat` and so on, for us to consider. – Nikita Kipriyanov Jun 02 '21 at 08:22
  • @MichaelHampton the selected disks are shown with green arrow. both SSD 850 evo. which are 931.5 GB in real size and advertised as 960 GB – Furkan Gözükara Jun 02 '21 at 10:11
  • @djdomi this is not a normal behavior. I also have raid on my personal computer and it uses all the storage available. disks have 931.5 GB real storage capacity. – Furkan Gözükara Jun 02 '21 at 10:11
  • @NStorm this screen is from bios. I am setting up raid in bios not in any operating system. – Furkan Gözükara Jun 02 '21 at 10:12
  • @MonsterMMORPG I understand that. This is the reason I've suggested you to actually try it from OS instead. – NStorm Jun 02 '21 at 10:37
  • @NStorm when I don't do raid I am able to use 931.5 GB. But as you suggested I plan to remove raid and compose again in windows server. Also on bios screen I am able to manually set size but I haven't tried that yet. I am trying to understand why default size is lower – Furkan Gözükara Jun 02 '21 at 11:21
  • @MonsterMMORPG I suggest you to stick with Linux. You can just get some Live distro on the USB drive, like SystemRescueCD for example. Linux has complete Intel RST Raid support with native metadata, but it allows to get more low level info to debug the reasons behind that. – NStorm Jun 02 '21 at 17:19
  • @NStorm i use windows server. I will delete raid from bios and compile from windows. Lets see what happens. waiting server provider to update kvm ip password. But I still didnt get answer why size is lower than what it is supposed to be. what causes this. why. – Furkan Gözükara Jun 02 '21 at 18:41

5 Answers5

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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

Robert
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  • look for what in the documentation? I did many raids on my personal computer before and they were able to use all the space. this is from my dedicated server – Furkan Gözükara Jun 02 '21 at 10:13
  • @MonsterMMORPG Hello, that is what we have seen many times with many RAID controllers. Look if this 3.8.0.1029 that you have does reserve space for metadata or if does make weird available space recalculation , maybe for block size changing. You can also create a unique partition of just one singe SSD and take note of the free space reported by the OS, then create the RAID, make the same partition on the RAID volume and compare the filesystem reported free space with the previous note. Five minutes test that could save you from headache – Robert Jun 02 '21 at 17:14
  • I can manually set size to 930 GB. would you suggest that? so this is only meta data problem not like anything system does to improve stability reliability etc? – Furkan Gözükara Jun 02 '21 at 17:18
  • @MonsterMMORPG I mean , just create 1 partition default assigning full space on one single SSD, and take note of the available free space in your OS for that partition. Then as free step, I would wipe the first 1GB of both the SSDs with an utility like this for windows www.lowlevelformat.info or dd or ddrescue for linux. Then create the RAID volume. Last make a default full partition with your OS on the RAID volume and compare the free space with the free space you had on the single SSD partition. – Robert Jun 03 '21 at 08:36
  • Beware: because wearing of SSDs , just and ONLY wipe the first 1% of the drive – Robert Jun 03 '21 at 08:39
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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.

chutz
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Barnabas Busa
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  • I know that. But it doesn't explain why 931.323 GB is reduced to 884.9 GB when creating Raid 1 – Furkan Gözükara Jun 02 '21 at 11:26
  • Its possible that your disk has some bad sectors, and gives some kind of warning to the raid controller not to allocate bad sectors to the raid array. – Barnabas Busa Jun 02 '21 at 11:28
  • No. I installed windows as no raid and did all kind of checks. All 931 GB of both disks are useable without any non useable sector. – Furkan Gözükara Jun 02 '21 at 11:29
  • Did you try different kind of RAID setups too? Do you get 1862G when you try RAID 0? – Barnabas Busa Jun 02 '21 at 11:35
  • Raid 0 is also lower size. it is 1769 GB. by the way I am able to set manual size but havent tested yet – Furkan Gözükara Jun 02 '21 at 17:19
  • I am really surprised, that you won't accept that the Vendors play with a factor of 1000 (because they can sell a 1TB drive instead of 1024GB) while the others working and the real world works with 1024 which ends up in a drive that's only around 930GB. Furthermore, it is a normal And Documented way that the Intel RST saves space for the Metadata, you can overwrite the size, but I have never tested it with live data. Remind windows it plays also with 1024, please see also the first place on https://en.m.wikipedia.org/wiki/Kilobyte about the 1000/1024 sentence – djdomi Jun 03 '21 at 08:09
  • @djdomi you don't really understand that it's not the issue. Drives are 1000GB, which turns out to be ~931.3GiB (as shown on OpROM already, and you can search for conversion factor of 1,074) , but the RAID0 array size should be then either 1000*2=2000GB or 931*2=1862GiB. Not the 1769G as it turns out. Same goes for 884.9G RAID1. The GB/GiB conversion can't apply twice. – NStorm Jun 03 '21 at 10:53
  • no not even when a second variable applies. there are 2 points here, the tr aversion of the 1000/1024 issue and additional as written but you don't want to understand is, that minus Metadata is the usable space left – djdomi Jun 03 '21 at 11:44
  • Nope. That's still not a point. And as already found out by OP it's about RST allocates 95% of space by default. It's not about the GB/GiB (1000/1024 as you call it) or metadata. – NStorm Jun 03 '21 at 19:46
0

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.

ExtremeMultiman
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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

José Luis Alcaraz
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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.

chutz
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  • That's not the coercion effect. The coercion effectively "rounds" a disk size down to nearest whole GiB. 884.9 GB is too odd value, it's not near some exact whole number of GiB. That's the GiB vs GB confusion, also including the displayed size of 951 GB while standard 1TB disks have 1953525168 of 512-byte sectors which is 951.5 GiB and they get coerced to 951 GiB. Notice the difference. – Nikita Kipriyanov Jun 08 '21 at 07:27
  • Would love to see the OP clarify the question. I took the subject asking "default capacity lesser than the disk size" to mean that the question is about why the 884.9GB v.s. 931GB (which is exactly 95% by the way). The OP seemed perfectly aware that 1TB advertised equals 931GiB. – chutz Jun 08 '21 at 13:53
  • @NikitaKipriyanov the Intel document I quoted clearly says that it `rounds down to 95% of the smallest physical disk`. I don't know what other coercion types are out there, but this one seems to do some very aggressive rounding. Its purpose I imagine is to avoid running into trouble when you buy a replacement drive only to find it is 1G smaller than the original one and so you cannot use it in the original raid. – chutz Jun 08 '21 at 13:59