I have got this message after update and reboot.

PANIC: VFS Unable to mount root fs on unknown-block (179,2)
Entering kdb (current=0xcb846c80, pid 1) due to Keyboard Entry

The problem is easy solvable at least for me.

So I boot on RescueCD – any Linux is OK in another PC

Then I run the filesystem repair (use your correct device name)

fsck /dev/sdb2

I had to run it multiple times, then I forced the check  fsck -f /dev/sdb2

And the file system was repaired.

Maybe there is s temporary solution. What I do is to sync file before reboot. So, I run command sync about 2 or 3 time before sudo reboot. Since this I have not seen again the error.

Update1: There is probably an influence of the overclock on the apperience of the file system corruption. Because I have seen the poblems always after higher load as for example update and upgrade.

Update2: Yes, when it is not overclock then they are no problems. Perhaps with another SD card it can work overclock also.

Update3: After some investigations and tests I found out that the original box I have used for Pi has venting holes only from down and therefore the I-O driver can over heat and it caused problems with ethernet, usb and SD card. Since I run it open I could make even the medium overclock without problem.

Update4: Raspberry failed It is sent for exchange to supplier see more info here.

Update5: The Raspberry was exchange by the supplier. New piece looks OK. Let’s hope.

Update6: The new piece has about 12 days of 7/24 running without any problem. It is even all the time overclocked (medium). I suppose if someone has still problem with stability then he should ask for exchange under the quarantine. Just I run it now out of the purchased original plastic case without any additional cooling with the SD card and power supply as the first one. I have not used any tweeks to the original Raspbian system.

Update7: It was running about 20 days 7/24 up to short electricity black-out and then againat least 14 days. It is solved. If you have some stability problem with USB you should contact your supplier and ask for exchange.