Wiping a server with sensitive data

Question

ORIGINAL QUESTION:

We have servers which we want to wipe and sell due to an environmentally friendly scheme, recycling, reducing carbon footprint etc. The servers have a raid configuration.

After doing some research, I am thinking of doing the following:

1. Use a Linux Live CD to boot into server
2. Use a strong password date +%s | sha256sum | base64 | head -c 32 ; echo and do a full disk encryption
3. Wipe the raid configuration using dd if=/dev/zero of =/dev/cciss/c0d0 bs=1M, dd if=/dev/random of =/dev/cciss/c0d0 bs=1M, dd if=/dev/zero of =/dev/cciss/c0d0 bs=1M
4. Wipe the HPA using hdparm -N /dev/cciss/c0d0, hdparm -N p[value goes here] /dev/cciss/c0d0
5. Wipe the DCO using hdparm --dco-identify /dev/cciss/c0d0, hdparm --dco-restore /dev/cciss/c0d0, hdparm --yes-i-know-what-i-am-doing --dco-restore /dev/cciss/c0d0
6. Bad sectors? sudo badblocks -n /dev/cciss/c0d0

Too little, okay, overkill?

The servers have sensitive data which must never be viewed by anyone.

Also, do I need to consider anything else, like wiping the RAM or any other possible area on the server where residue may be left?

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UPDATE 1:

All disks are magnetic 2.5" scsi disks.

Answer 1

There is no need to do full disk encryption in step 2. Simply do

dd if=/dev/zero of=/dev/sda bs=1M

where /dev/sda is the hard disk device (change it to whatever your disk is called). You might also want to change the block size.

If you don't like the overwrite by 0s (there are people who claim that such overwrites aren't enough to actually make the old values unrecoverable, though you need special hardware to recover the overwritten data), use /dev/urandom instead, for as many times as you deem secure. You can also use the program shred.

You could probably stop after step 2.

I'm not sure why you overwrite your RAID config block 3 times in step 3. If you overwrite the whole disk in step 2, it should already be gone. Also, AFAIK, it contains no sensitive information.

I'm also not sure about your step 4. Why do you think that this wipes the HPA? Shouldn't you do this before step 2, disable the HPA by making it 0 blocks long, and then overwrite it in step 2?

In step 6, you're scanning for bad sectors. You're not doing anything else. But since you're already scanning for them, you might as well use badblocks -w and do a destructive scan, which will overwrite every sector and make step 2 unnessecary.

Hard drives set aside a few sectors that can be swapped for defective sectors. These defective sectors are often still readable and they might contain sensitive information. So you should take care of those, too. They do not get overwritten in step 2 (nor, I think, in step 6)

Answer 2

If you don't absolutely need to sell the drives, pull them and send them to a recycler for shredding. Physically destroying the drives is a much more secure (and faster) way of dealing with them than all the iterations you're going through. There will be info on each fragment of the drive and it is technically readable, but those fragments are small and reassembling them into anything meaningful is a very daunting task. If you shred multiple disks in one batch, the signal-noise ratio is too high to have any meaningful chance of getting your data off those platters.

If you want you can go through step 1, making the data encrypted before it's destroyed, that would make that task impossible.