[Solved]Harddrive disappears or got deteched in FreeBSD

Have you experienced these computer problems like mine before? You got some error messages that your system cannot read your harddrives, or your harddrives suddenly got detached by your system. You have no clue why it happens because it is a fairly new harddrive. Before you decide to discard, return or RMA your harddrive, let me share you my experience first because it may save your harddrive (and your bank).

Recently, I found several harddrive related computer problems in my FreeBSD systems. These includes:

Symptom: Harddrive seems failing

When I boot the computer, it threw me the following messages:

ad0: FAILURE - READ_DMA status=51 ready ,DSC,ERROR error=40 uncorrectable LBA=sector
ad0: FAILURE - READ_DMA status=51 ready ,DSC,ERROR error=40 uncorrectable LBA=sector
ad0: FAILURE - READ_DMA status=51 ready ,DSC,ERROR error=40 uncorrectable LBA=sector

If you miss these messages during the boot process, you can review these messages using the following command:

sudo dmesg | grep ad | less

Symptom: Harddrive is disappeared or got detached

When I tried to test the harddrive using dd, e.g.,

dd if=/dev/random of=/dev/ad0

(This command will wipe the entire disk with random data until the disk is full. The reason why I do it because I want to test every single sector of the disk.)

It gave the following message:

dd: /dev/ad0: open: I/O error

and I checked the /dev/ad0, e.g.,

ls -al /dev/ad0

The file was disappeared.

Apparently, the device was detached by the system automatically.

So, how do you solve this computer problem? Here are few methods I recommend you to try:

Solution: Check the SMART Status

You can check the SMART status of the harddrive using the following command:

smartctl -a /dev/ad

Make sure that the test result is PASSED.

If you don’t have smartctl installed, it is available in the following port:


Solution: How do you connect your harddrive?

Sometimes, connecting the harddrive through PCI card can cause issue (at least in my case). After connecting the harddrive to a different port, such as switching from port 1 of the card to port 3 of the motherboard, the computer problem is solved and gone. If the computer problem still exists, the next thing I will try is to connect the harddrive using USB or firewire. You can do it by getting an harddrive enclosure.

Solution: Replacing harddrive cables

Old harddrive cables can be the source of the computer problems too. Since the temperature inside the computer chassis is high, and the harddrive cables are usually bended, these can soften the cable and may break the metal wire inside the cable. Try replacing it by new cables and see the computer problem is gone or not. Also, check the power adapter as well. Sometimes this computer problem is caused by loose power connectors.

Solution: Have you installed any new harddrive recently?

Sometimes, the system will behave abnormally because of newly installed hardware. It can be any reason such as conflicting hardware etc. Recently, I installed a PCI flash card adapter, which caused the system very unstable. After I removed the card, the computer problem is solved and gone.

Solution: Is your Motherboard doing okay?

Although it is not likely, but this computer problem can caused by the burned motherboard. Sometimes, if a mother board is getting old, it can be unstable and not reliable (Heavy usage such as gaming can generate high temperature, which will decrease the life span of a motherboard). To determine the root of the computer problem, I will replace a motherboard and test the system again.

How do you know if your system is stable or not?

Here are few things I usually do to test the stability of a system:

1. Run the machine for at least a week.

2. Wipe all non-system harddrives using dd:

sudo dd if=/dev/random of=/dev/ad0 &
sudo dd if=/dev/random of=/dev/ad2 &
sudo dd if=/dev/random of=/dev/ad4 &


where ‘&’ at the end of the command means running it in background.

3. If possible, always keep your system in a cool place such as basement. It helps to keep the harddrive healthy.


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