0

I have a CentOS 7.7 server which has a vhd /dev/sdc mounted (format-type= btrfs); it contains data.

I attached a empty vhd to the VM, /dev/sdd (I didn't partition this disk using fdisk)

lsblk command lists the attached disk but no mount point.

used, mdadm --create /dev/md0 --level 0 --raid-devices=2 --name=/data-disk /dev/sdc /dev/sdd

Output:

mdadm: cannot open /dev/sdc: Device or resource busy

Question:

  • Will the data from the disk /dev/sdc get wiped out when I try to create a RAID0 array?

  • I can issue umount /dev/sdc and issue the mdadm --create command, but is that a proper approach to do this.

=== in case of successful RAID0 creation ===

Below command would be executed:

mkfs.btrfs /dev/md0

Editing the /etc/fstab, with the uuid info

===

Trying to add two disks to RAID0, one is already setup as backup, which has data. The new one is attached, could see the disk using lsblk, but

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sdc      8:32   0    100G  0 disk /cass_backup
sdd      8:48   0    100G  0 disk

df -h

/dev/sdc        100G  82G  20G  20% /data_disk

How does the distribution of data between mounted and unmounted disk done? Do I need to mount the new one (/dev/sdd) first?

1 Answer 1

1

Transforming a single disk to a RAID0 array will break your filesystem. More precisely you would first need to carefully distribute the data of /dev/sdc onto both disks.

You can create a RAID1 array more easily, since RAID1 has identical data on both disks: cf. Converting a single drive system to RAID.

Fortunately you are using btrfs, which combines the power of a filesystem, RAID and LVM. So add the second disk to your btrfs and convert it to a RAID0 array.

Edit: In your case the conversion to RAID0 is as simple as: mounting your original btrfs filesystem (let say on /mnt). Expand the filesystem:

mount /dev/sdc /mnt
btrfs device add /dev/sdd /mnt
btrfs balance start -dconvert=raid0 -mconvert=raid0 /mnt

The data on /dev/sdd will be lost, but data from /dev/sdc will remain.

2
  • Trying to add two disks to RAID0, one is already setup as backup, which has data. The new one is attached, could see the disk using lsblk, but NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sdc 8:32 0 100G 0 disk /cass_backup sdd 8:48 0 100G 0 disk df -h /dev/sdc 100G 82G 20G 20% /data_disk How does the distribution of data between mounted and unmounted disk done? Do i need to mount the new one (/dev/sdd) first?
    – Tim
    Dec 11, 2019 at 21:52
  • 1
    I added more info to the answer. Dec 12, 2019 at 0:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.