I am working with the RAID6 configuration with 4 disks involved, each of size 8TB. Hence the total capacity = (n-2) * s, where n = number of disks and s = size of disks. So in my case it is 16TB.

Below is the information before the dd operation is performed:

df -h /mnt/raid6/

Filesystem      Size  Used Avail Use% Mounted on
/dev/md0         15T  1.1G   14T   1% /mnt/raid6

dd operation performed:

dd if=/dev/zero of=/dev/md0 bs=1G count=5 oflag=dsync

5+0 records in
5+0 records out
5368709120 bytes (5.4 GB) copied, 76.7451 s, 70.0 MB/s

Information after performing dd operation:

df -h /mnt/raid6/

Filesystem      Size  Used Avail Use% Mounted on
/dev/md0         64Z   64Z   15T 100% /mnt/raid6

My confusion is here, when I have performed a write operation with 5GB file on the RAID6 devices, why the output is shown as Used = 64Z?

  • Did you do that dd while /mnt/raid6 was mounted? – AlexP Dec 7 '16 at 9:46
  • You corrupted your filesystem. – frostschutz Dec 7 '16 at 9:50
  • @AlexP : yes, the operation was performed after mounting, /mnt/raid6. – Here_2_learn Dec 7 '16 at 10:00
  • Your file system is corrupt. You need to mkfs again. I hope you did not have any data there. – AlexP Dec 7 '16 at 10:02

What you did is completely erasing all file system metadata, thus irrevocably making it unusable.

You have to do the partitioning again or better to re-create the array according to this guide.

If you want to check the filesystem on the array is doing fine, just create a file on the mounted array e.g.:

dd if=/dev/zero of=/mnt/raid6/testfile bs=1M count=8192
  • thanks for response, the reason for doing dd operation is to check the read/write operation on that disk/raid after creation of RAID. Is that the right way to do or any other proper way to check read/write operations after RAID creation. – Here_2_learn Dec 7 '16 at 10:07

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