Testing hard drives for bad blocks

Badblocks tests block devices such as hard drives and USB memory sticks for bad blocks. It is one of the first diagnostic tools I use when facing a problem of unknown origin.

First step is to boot the box with a live distribution. Open a terminal, become root (everything in this article must be done as root) and see if your live distro automatically mounted the hard disk. In one case, I saw:

# df -T
Filesystem    Type    Size  Used Avail Use% Mounted on
none       unionfs    2.9G  266M  2.7G   9% /
/dev/sdb1      xfs    7.8G  4.5G  3.4G  57% /media/hd6
/dev/sdb6      xfs    142G  103G   40G  73% /media/hd7

If you need more information — perhaps something looks suspicious — gparted (run as root) is a fuller featured tool.

In the above example we see that the root partition on the hard disk, /dev/sdb1, is mounted as /media/hd6. So we unmount it, using the mount point, not the device name: umount /media/hd6.

Once identified and unmounted, run badblocks as root:

# badblocks -sn /dev/sdb

Naturally, replace sdb1 with your device name. Bad blocks identified, if any, will be shown on standard output.

The -n option specifies nondestructive testing, which is slow. If there’s nothing on the device worth saving, substituting -w for -n will perform a faster destructive test.

If you want to test a mounted device that can be unmounted — say, a USB stick — you can do that without having to use a live CD. Just unmount the device first, as root:

# umount /dev/sdb

Again, substitute your device name for “sdb”.


About Warren Post

So far: Customer support guy, jungle guide, IT consultant, beach bum, entrepreneur, teacher, diplomat, over-enthusiastic cyclist. Tomorrow: who knows?
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One Response to Testing hard drives for bad blocks

  1. Pingback: Fixing a damaged filesystem | A maze of twisty little passages

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