On 5/26/05, Michael Hennebry <hennebry@xxxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 25 May 2005, Deron Meranda wrote: > > > If nothing else you can always wipe the drive the forceful way; > > boot into Linux (or the recovery disk) and do something like, > > > > dd if=/dev/zero of=/dev/hda bs=512 > > > > **Warning, that will delete EVERYTHING on the hard drive! > > Is bs=512 necessary or useful? It's good practice to always specify a blocksize when copying to a block device (such as /dev/hda). The blocksize is how many bytes it writes with each "transaction". It should ideally be exactly (or a multiple of) the actual physical device's block size (which for ATA disks is almost always 512 bytes). If you specify 4096 for instance the writing may be faster (although there is a point of diminishing returns for making bs too large). > Would cp /dev/zero /dev/hda do the same thing? No. cp operates at the filesystem level, while dd operates at the device level. cp actually wouldn't work because /dev/hda is not a filesystem (although it contains an image of a filesystem which you access by mounting it first). Also even if cp could work, you still might want to erase the non-filesystem portions of your disk (e.g., partition tables, boot blocks, swap partitions, LVM structures, etc.) dd lets you scribble across the whole storage media without regards to filesystems, partitions, or anything. Note that when scrubbing a disk in this fasion, it may take a very long time for the dd command to complete on today's large hard drives (hour or so). If you don't care about erasing all data, sometimes you just want to "soft" erase the disk which means clearing the partition table, boot sectors, etc. You can quickly do that with, dd if=/dev/zero of=/dev/hdz bs=512 count=64 And future OS installs (whether Linux or Windows) would then see the disk as being an uninitialized from-the-factory disk and format it (which helps greatly if/when you have a corrupted partition table that crashes the OS installers). However, if you're selling your computer do the dd one the whole disk. That's also useful to do if you suspect you have some bad blocks/tracks on the disk as it is one easy way to insure that you've tried writing to every single sector. -- Deron Meranda
