How to securely wipe your ReadyNAS

Vendor tools also allow you to write zeros to every sector of the drive.

mdgm wrote:

If you do a secure delete of your files they would be gone. If you do a factory default with the drives in place that would make data recovery even more difficult (if it wasn't already impossible). If you're wanting to sell your drives (not with your NAS) you could hook them up to your PC and format them to use NTFS as I suggested earlier. Most people would assume, that they were connected to a Windows PC and wouldn't suspect they were formatted using the EXT3 filesystem

Well I just did a normal delete of most of my files using a mapped drive from a PC. These were the files that I was most concerned with as they contained backups of several systems with potentially some sensitive information. The files that I am deleting now using srm are ones I'm not so concerned with. (so perhaps I did this backwards).

I'm not opposed to using a PC to format my drives but if I can avoid it I would prefer not to. And I was thinking that there may be other ReadyNAS users out there who bought the same drives that I did and are looking for some spares so trying to hide their history would not work in that case.

So my question is whether srm will have any impact on the available free space where my previously deleted files potentially still exist. If it does then I think that, along with a factory reset would put my mind at ease. But if the free space is not overwritten securely then I need to find a way to do that.

StephenB wrote:
Vendor tools also allow you to write zeros to every sector of the drive.

I'm not quite sure what you mean by Vendor Tools. How would I go about doing that?

You would hook your drives up to an internal SATA port in your PC and say boot off the Ultimate Boot CD. You could then use disk wiping tools such as DBAN or vendor tools e.g. SeaTools for SeaGate disks to securely wipe the disks.

OK I see... yes this is the step I'm trying to avoid if possible.
So I guess that means srm does not take care of the free space but just the actual files it deletes?

srm would just delete files, I think. A factory default would wipe the partition table off the disks and create a new partition table and create a new volume.

Update:
I realized that I was going to spend many hours or days waiting for srm to securely wipe several hundred GB of media files that I don't really care about. So I decided to abort that process after 6 hours. The files I care about are already deleted and just need to be wiped somehow. Of course there are many theories and opinions about this... but the idea of just overwriting the data blocks by filling the drive space with zeros makes sense to me. And I am not some secret government body with classified secrets to hide. I just don't want some stranger to be able to recover my personal info, photos, or passwords.

I just came across the following suggestion as a way to write zero filled files to every free block on the disk and then delete them:

dd if=/dev/zero of=hugefile; sync; rm hugefile; sync

So I could probably be happy with something like that... but then I noticed that the OP of this thread already addressed the free space question with the sfill command.

sfill -v /c/

That's running now with the full 38 passes using random data, so I expect that could run a while.
When that's done I believe I will run it a second time with the -l switch for 2 more passes... just for fun.

sfill -l -v /c/

Then I will do the factory reset. I think after that I'll feel pretty good about it without having to plug each drive into a PC and reformat etc.
And if I can sell each drive separately all the better. I will probably keep at least one for myself.

FYI - Here is some additional reading I came across on the subject of dd and sfill in case anyone is interested:
https://bbs.archlinux.org/viewtopic.php?id=83672
http://www.noah.org/wiki/Dd_-_Destroyer_of_Disks
http://www.ubuntugeek.com/tools-to-delete-files-securely-in-ubuntu-linux.html

I really appreciate the input mdgm and of course many thanks to Tristan for the detailed instructions.

xyxoxy wrote:
OK I see... yes this is the step I'm trying to avoid if possible. So I guess that means srm does not take care of the free space but just the actual files it deletes?

From the srm man page:

Some of your data might have a temporary (deleted) copy somewhere on the disk. You should use sfill which comes with the secure_deletion package to ensure to wipe also the free diskspace. However, If already a small file aquired a block with your precious data, no tool known to me can help you here. For a secure deletion of the swap space sswap is available.

Thanks again tristan...

For anyone still following along - I can report that trying to use sfill in secure mode (full 38 wipes with random data) was going to quite literally take a couple of weeks to complete on my 1TB array. I think it had only completed something like 36GB after 24 hours. So I decided to abort it and go with a couple variations of the less secure options:

sfill -l -v -z /c/
sfill -f -l -v /c/

These took several hours each but at least hit the entire array with a few overwrites.

I did also erase the swap space using sswap as follows:
Identify your swap partitions

cat /proc/swaps

disable them

sudo swapoff /dv/hdc2
sudo swapoff /dv/hde2
sudo swapoff /dv/hdg2

wipe them

sudo sswap /dev/hdc2
sudo sswap /dev/hde2
sudo sswap /dev/hdg2

These only took maybe 10-15 minutes each to complete.

Now on to the factory reset and then finally install the new drives!