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#1 2022-11-27 12:53:22

seolha314
Member
Registered: 2022-11-27
Posts: 3

[SOLVED] Madam incorrect array and used dev size

I've combined 8 16tb drives in raid 6. In my theory the array should report its size 96.00tb, but instead mdadm reports the total array size 87.32tb, not 96tb. Also, It says I have 14.55tb of used dev size.

$ sudo mdadm --detail /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Fri Nov 25 14:53:10 2022
        Raid Level : raid6
        Array Size : 93754475520 (87.32 TiB 96.00 TB)
     Used Dev Size : 15625745920 (14.55 TiB 16.00 TB)
      Raid Devices : 8
     Total Devices : 8
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Sun Nov 27 11:57:05 2022
             State : clean
    Active Devices : 8
   Working Devices : 8
    Failed Devices : 0
     Spare Devices : 0

            Layout : left-symmetric
        Chunk Size : 512K

Consistency Policy : bitmap

              Name : XXXXXXX
              UUID : 8f8eaee0:2b760d64:1fec58e7:ae9f0b0b
            Events : 27584

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       1       8       17        1      active sync   /dev/sdb1
       2       8       33        2      active sync   /dev/sdc1
       3       8       49        3      active sync   /dev/sdd1
       4       8       65        4      active sync   /dev/sde1
       5       8       81        5      active sync   /dev/sdf1
       6       8       97        6      active sync   /dev/sdg1
       7       8      113        7      active sync   /dev/sdh1

fdisk shows the same sectors for each partition on the disk.

$ for i in a b c d e f g h; do sudo fdisk "/dev/sd$i" -l ;done
Disk /dev/sda: 14.55 TiB, 16000900661248 bytes, 31251759104 sectors
Disk model: MG08SCA16TE
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 3CAD746E-3B91-1F46-8BF2-0FA467D9EA4E

Device     Start         End     Sectors  Size Type
/dev/sda1   2048 31251759070 31251757023 14.6T Linux RAID
Disk /dev/sdb: 14.55 TiB, 16000900661248 bytes, 31251759104 sectors
Disk model: MG08SCA16TE
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 23797260-8081-4541-A645-574EB9660ED6

Device     Start         End     Sectors  Size Type
/dev/sdb1   2048 31251759070 31251757023 14.6T Linux RAID
Disk /dev/sdc: 14.55 TiB, 16000900661248 bytes, 31251759104 sectors
Disk model: MG08SCA16TE
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 89A823DE-0662-9D49-B100-440508C4C05F

Device     Start         End     Sectors  Size Type
/dev/sdc1   2048 31251759070 31251757023 14.6T Linux RAID
Disk /dev/sdd: 14.55 TiB, 16000900661248 bytes, 31251759104 sectors
Disk model: ST16000NE000-2RW
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 37365809-1E64-F748-B4B4-6BD675969198

Device     Start         End     Sectors  Size Type
/dev/sdd1   2048 31251759070 31251757023 14.6T Linux RAID
Disk /dev/sde: 14.55 TiB, 16000900661248 bytes, 31251759104 sectors
Disk model: MG08SCA16TE
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 453FE0BD-047A-BC4E-9221-E21DAD8FAE10

Device     Start         End     Sectors  Size Type
/dev/sde1   2048 31251759070 31251757023 14.6T Linux RAID
Disk /dev/sdf: 14.55 TiB, 16000900661248 bytes, 31251759104 sectors
Disk model: ST16000NE000-2RW
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 81416E80-49BC-6949-9122-4ECD6BDA6604

Device     Start         End     Sectors  Size Type
/dev/sdf1   2048 31251759070 31251757023 14.6T Linux RAID
Disk /dev/sdg: 14.55 TiB, 16000900661248 bytes, 31251759104 sectors
Disk model: WUH721816ALE6L4
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 511C012C-EA45-D042-8825-49D7FEF57277

Device     Start         End     Sectors  Size Type
/dev/sdg1   2048 31251759070 31251757023 14.6T Linux RAID
Disk /dev/sdh: 14.55 TiB, 16000900661248 bytes, 31251759104 sectors
Disk model: WUH721816ALE6L4
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: E3D62C63-87CB-CF4D-B8E5-BC69B3672D25

Device     Start         End     Sectors  Size Type
/dev/sdh1   2048 31251759070 31251757023 14.6T Linux RAID

Here is my /proc/mdstat.

$ cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10]
md0 : active raid6 sdh1[7] sdg1[6] sdf1[5] sde1[4] sdd1[3] sdc1[2] sdb1[1] sda1[0]
      93754475520 blocks super 1.2 level 6, 512k chunk, algorithm 2 [8/8] [UUUUUUUU]
      bitmap: 0/117 pages [0KB], 65536KB chunk

unused devices: <none>

Last edited by seolha314 (2022-11-27 13:31:53)

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#2 2022-11-27 13:00:59

Zod
Member
From: Hoosiertucky
Registered: 2019-03-10
Posts: 595

Re: [SOLVED] Madam incorrect array and used dev size

In my theory the array should report its size 96.00tb

Perhaps you should show your work?

How did you come to that conclusion?

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#3 2022-11-27 13:08:03

seolha314
Member
Registered: 2022-11-27
Posts: 3

Re: [SOLVED] Madam incorrect array and used dev size

Zod wrote:

In my theory the array should report its size 96.00tb

Perhaps you should show your work?

How did you come to that conclusion?

8 times 16tb minus two drives for parity, that returns 96tb, right?
And I have used this command to make an array:

# mdadm --create /dev/md0 --level=6 --raid-devices=8 /dev/sd[a-h]1

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#4 2022-11-27 13:19:50

Zod
Member
From: Hoosiertucky
Registered: 2019-03-10
Posts: 595

Re: [SOLVED] Madam incorrect array and used dev size

RAID6
*Raw Storage: 128.0 TB / 128000.0 GB
*Usable Storage: 87.3 TB / 89407.0 GB
RAID6 uses two disks for Parity and requires at least four drives to be used.


*Usable storage is the actual post-format amount where kilo = 1024, not 1000

https://www.servethehome.com/raid-calculator/

This might help, some light reading...
https://mirrors.edge.kernel.org/pub/lin … /raid6.pdf

Last edited by Zod (2022-11-27 13:20:32)

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#5 2022-11-27 13:28:52

seolha314
Member
Registered: 2022-11-27
Posts: 3

Re: [SOLVED] Madam incorrect array and used dev size

Oh, a common mistake with TB and TiB...

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