Sanitizing/shredding RAID 5 array...

[chillum]

Hi there,

My company is about to sell a used Compaq 1850r Server. I am concerned about making sure that all data on this machine is completely erased before handing it over to someone else. The data is stored on an external RAID 5 data array connected to a Smart Array Controller. I plan to use a program called disk sanitizer to erase all data on the drives. This is a DOS based program that erases a hard drive in a manner consistent with Peter Gutmann's recomendations. As this procedure can be quite lengthy, I would much rather run it on the arrays as they are configured rather than reconfiguring each of the drives to stand alone; then wiping them individually. (although this is the procedure I am most sure would completely erase the data). What I want to know is: will every sector on each HD in the array actually be overwritten when I run such a sanitizing program on it?
I have two arrays configured: An internal mirrored array with 2 18 GB HDs for the OS and working space, and an external enclosure with 3 more 18 GB drives configured as a RAID 5 array. I assume that he mirrored array will be no problem, as the data should be overwritten on both drives simultaneously(right? ). I also assume that something similar will happen with the RAID 5 array, but since I am not entirely sure about how RAID 5 is implemented I am not sure. Is the parity data just a mirrored image of the data from the other drives, or is it some type of calculated value(like a cheksum)? If the data is just mirrored and split onto the other two drives it seems logical that it would be completely overwritten in the process. If it is derived values that are stored I am not so confident that every byte will be replaced in each pass.
If anyone who knows more about how this raid 5 controller works can give me any advice I would greatly appreciate it.
Thank you.
Forest.

 

[dieselfreak]

The following is a very simple way of showing what happens to writes onto a 3 disk RAID5 volume. (3 disks is also the minimum requirements for RAID5)

P=Parity D=Data
_______________________________
1¦2¦3 <- Drive#

D¦D¦P <- First Write
D¦P¦D <- Second Write
P¦D¦D <- Third Write
D¦D¦P <- Forth Write
_______________________________

So basically the partiy infomation which can be used to re-create the data, in the event of disk failure, is writen to each drive in the RAID set in turn.

Unlike RAID 4 which has a dedicated physical disk for parity.

As for erasing the data on the RAID set...

I'd simply use the ARRAY CONFIGURATION UTILITY delete the orginal arrays and then create a new configuration different to the first. This will cause an initalisation of the disks to occur. If this isn't enough, use the utility CREATEFIL.exe on the Res-Kit to create a 4GB file and copy and paste the file to the new drives until full......


Of course if your really that worried about data-protection do what some of the Government bodies do in the U.K. Get a Drill/Hammer and let lose... ;-)

If you'd like any more detailed information please let me know with another post and i'll reply


Cheers

diEAselfReAK

 

[samuelma]

Before you create the second array move the disks around.