Securing a single HDD from a retired RAID 5 array

Solution 1:

The data would be relatively safe from being recovered given a couple of things. The RAID5 set was more than 3 drives and the drives are not going to be sold to the same person/company. But even then a close look at the drive's data could contain strings etc.

If the drives are going to one person/company then it's possible to force the RAID back together in a degraded state. From there you can recover the LVM metadata and reconstruct the logical volumes.

So I'd do a quick wipe using dd and call it a day. Using dd if=/dev/zero of=/dev/sdb bs=1M is probably the fastest way and is a good enough wipe to make whatever is on the drives now unrecoverable. Just make sure you change the of= device to be the appropriate drives.

If you're really paranoid you can use a better wiping tool but it's not really necessary unless there are some regulations on the data that you were storing.

Solution 2:

If it is a boot disk, you may use DBAN tool for a secure wipe. http://www.dban.org/

Solution 3:

If you are running Linux, there are several commands that can be used to wipe a disk :

dd if=/dev/urandom of=/dev/sdx
shred -vn /dev/sdX
badblocks -c 10240 -s -w -t random -v /dev/sdx

where sdx is your HDD. These commands will fill the HDD with random data and are therefore very long to run (approx 1min/GB). You may also use /dev/zero (instead of /dev/urandom) which is faster but a little less secure.

You may also wipe the first megabytes (which imho provides good enough security) of you HDD with the following command :

dd if=/dev/zero bs=1000000 count=100 of=/dev/sdx

If you sell the two disks separately, it is quite unlikely that someone is able to extract data from one them so you can sell them without wiping data.