On Wed, Jun 16, 2010 at 08:43:29PM +0100, Harry Palmer wrote:
> Beginning my effort to encrypt a 300GB drive in a 64bit Ultrasparc,
> I followed these initial steps:
>
> 1. used disklabel to create a single slice "a" on the drive
>
> 2. made a file system with newfs (is it necessary to have so many
> backup superblocks?)
Why don't you just use softraid(8)? No need for a filesystem, and this
particular use-case (encrypted disk) is in the EXAMPLES section of the
man page.
> 3. mounted sd2a on "/home/cy" and touched it with an empty file
> "/home/cy/cryptfile"
>
> 4. zeroed out the file (and efectively the drive) with
> "dd if=/dev/zero of=/home/cy/cryptfile bs=512"
Again, why don't you work with the disk directly? Doing "dd if=/dev/zero
of=/dev/rsd0a conv=notrunc" would work fine. ("notrunc" is useful to
wipe the last bytes if you use a different blocksize - 512 is the
default, but on the low side.)
> Now I have:
>
> # disklabel sd2a
> and:
>
> # df -h
> Filesystem Size Used Avail Capacity Mounted on
> /dev/sd0a 1007M 44.8M 912M 5% /
> /dev/sd0k 247G 2.0K 235G 0% /home
> /dev/sd0d 3.9G 6.0K 3.7G 0% /tmp
> /dev/sd0f 2.0G 559M 1.3G 29% /usr
> /dev/sd0g 1007M 162M 795M 17% /usr/X11R6
> /dev/sd0h 5.9G 212K 5.6G 0% /usr/local
> /dev/sd0j 2.0G 2.0K 1.9G 0% /usr/obj
> /dev/sd0i 2.0G 2.0K 1.9G 0% /usr/src
> /dev/sd0e 7.9G 7.7M 7.5G 0% /var
> /dev/sd2a 275G 275G -13.7G 105% /home/cy
>
>
>
> I have no understanding of this. I've never seen a df output
> that tells me I'm using 13GB more space than the drive is
> capable of holding.
This is perfectly fine. newfs reserves, by default, 5% of all available
space for use by the root user only. This is useful in two ways: it
means root can squeeze a bit more data on the filesystem, and it
prevents the performance degradation that comes with completely filling
up a (ffs) filesystem.
What you are seeing is that the *entire* disk has been used, including
reserved space.
Joachim
