On Wed, Jun 16, 2010 at 05:45:40PM -0400, George Morgan wrote:
> Quoting Harry Palmer <tumblew...@fast-mail.org>:
>
> >Hi there.
> >
> >I'm fairly new to openbsd and I'm hoping someone with better
> >understanding than me of how its disk handling works can help.
> >
> >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?)
> >
> >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"
> >
> >
> >Here's the (eventual!) output of (4):
> >
> > /home/cy: write failed, file system is full
> > dd: /home/cy/cryptfile: No space left on device
> > 576520353+0 records in
> > 576520352+0 records out
> > 295178420224 bytes transferred in 19810.722 secs (14899932 bytes/sec)
> >
> >
> >
> >Now I have:
> >
> > # disklabel sd2a
> > # /dev/rsd2a:
> > type: SCSI
> > disk: SCSI disk
> > label: MAW3300NC
> > flags: vendor
> > bytes/sector: 512
> > sectors/track: 930
> > tracks/cylinder: 8
> > sectors/cylinder: 7440
> > cylinders: 13217
> > total sectors: 585937500
> > rpm: 10025
> > interleave: 1
> > boundstart: 0
> > boundend: 585937500
> > drivedata: 0
> >
> > 16 partitions:
> > # size offset fstype [fsize bsize cpg]
> > a: 585937200 0 4.2BSD 2048 16384 1
> > c: 585937500 0 unused
> >
> >
> >and:
> >
> > # ls -l /home/cy
> > total 576661216
> > -rw-r--r-- 1 root wheel 295178420224 Jun 16 03:39 cryptfile
> >
> >
> >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.
> >
> >I ask here because there's obviously potential for me to lose
> >data somewhere down the line. I'll be grateful if anyone can
> >explain where I've gone wrong.
>
> I've seen the greater than 100% full on a UFS? filesystem before when
> you exceed the size of the filesystem. There is space in the
> filesystem for "lost+found" and all those superblocks? you were
> complaining about that can get overwritten if you write too much to a
> partition.
Spoace for superblocks and other metadata is subtracted from available
blocks. lost+found is an ordinary directory.
>
> So setting up your "dd" to actually stop before you overfill the
> filesystem is what you need to do. (using bs=# count=# ... info you
> can get before you start initializing your file with the df command
> without the "-k or -h" to get number of blocks and block size)
>
> I'm sure the fine people on these lists will correct me if I'm wrong
> in my assumptions... :-)
You are wrong, there;s no such thing as overfilling a filesystem. It's
just the 5% reserved for root. An ordinary user runs out earlier. It's
in the FAQ.
-Otto
>
> George Morgan
