Here is the output for fdisk -l:

ubuntu@ubuntu:~$ sudo fdisk -l 

WARNING: GPT (GUID Partition Table) detected on '/dev/sda'! The util fdisk doesn't support GPT. Use GNU Parted.

Disk /dev/sda: 2698.6 GB, 2698581639168 bytes 255 heads, 63 sectors/track, 328083 cylinders, total 5270667264 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000

Device Boot Start End Blocks Id System /dev/sda1 1 4294967295 2147483647+ ee GPT

Disk /dev/sdb: 5397.2 GB, 5397163278336 bytes 255 heads, 63 sectors/track, 656167 cylinders, total 10541334528 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000

Disk /dev/sdb doesn't contain a valid partition table

I can mount /dev/sdb.

sudo mkdir /media/raid0/
sudo mount -t ext4 -v  /dev/sdb /media/raid0

But I failed to mount sda:

sudo mkdir /media/raid1/
sudo mount -t ext4 -v  /dev/sda /media/raid1

Here is the error message: mount: /dev/sda already mounted or /media/raid1/ busy

I want to mount /dev/sda and backup the data. Please let me know if you have any idea. Thanks in advance.

  • Why are you not using RAID tools (mdadm) to mount a RAID array?
    – user535733
    Nov 20 '19 at 4:28

From the name, are we to assume that this is a raid set? With sda and sdb in the raid configuration? If so, then if the virtual disc is mounted, then you can't (and shouldn't try) to mount the individual raid components separately...

... UNLESS This is a RAID-1 configuration.

Then you can temporarily split the raid pair and take one leg off line. That does allow you to split the mirror pair, take one part offline, back it up, bring it back on line and add it back to the mirror pair in catch up mode.

This is complex. I have watched an experience sysadmin do this and get the command to bring the now older offline mirrored disk back online, but as the primary, this making what was the primary the secondary and casually wiping out any changes. His system crashed soon after with massive database corruption. So, lets be careful out there!

If this is what you are trying to do, you need to lock and quiesce any databases or programs you have running to ensure that the raid set is 'quiet' when you do the split. Otherwise your offline copy is in an inconsistent state. It will be problematical to restore. Oracle enterprise databases can do this, but I am not sure others can. Nowadays you use Oracles built in backup mechanisms to do this task and forget about all that nasty raid management.

But think very carefully about what you are doing. Using RAID sets like this is fraught with errors and there are normally better ways of doing the same thing.

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