A systems administrator has added new disks to a Linux server and configured them as a RAID 6 array, /dev/md0. The administrator created a partition and an XFS filesystem on the array. To make the storage persistently available, an entry was added to /etc/fstab. After rebooting, the administrator notices that applications cannot write to the target directory /data, and the output of df -h does not list the new filesystem. However, lsblk shows the /dev/md0 device. What is the MOST likely cause of the "drive not available" issue?
The XFS filesystem on /dev/md0 is corrupt.
The RAID array is degraded and in a read-only state.
The /etc/fstab file contains a syntax error.
The host bus adapter (HBA) firmware is incompatible with the drives.
The correct answer is that the /etc/fstab file contains a syntax error. The scenario indicates the operating system can see the underlying block device (/dev/md0 is visible to lsblk), but the filesystem is not mounted and available for use (it is missing from df -h output). Since a reboot was performed after adding an entry to /etc/fstab, the filesystem should have mounted automatically. Its failure to do so strongly suggests an error in the /etc/fstab entry, such as an incorrect device name, a typo in the filesystem type, or incorrect mount options, which prevents the system from processing the line correctly during boot.
A degraded RAID array would typically still be mountable (though possibly in read-only mode) and would appear in the df -h output. The primary symptom here is a complete failure to mount.
Filesystem corruption is possible but less likely on a newly created filesystem than a simple configuration file typo. A corrupt filesystem would also likely produce specific I/O errors in the system logs during the mount attempt.
An HBA firmware incompatibility would likely prevent the operating system from detecting the physical drives or the RAID array itself, meaning /dev/md0 would not appear in lsblk output.