sparse image

Vincent Hoffman vince at
Wed Jun 23 10:54:52 UTC 2010

On 23/06/2010 11:26, Aiza wrote:
> Is there an equivalent of the MAC sparseimage on FreeBSD?
If you mean you would like to make a sparse file and attach it using
mdconfg then
dd if=/dev/zero of=/path/to/outfile bs=1M seek=1024 count=0
This will give you a sparse file that reports a gig in size, but only
uses whats actually in use.
you can then use mdconfig(8) to allow this to be partitioned formatted
and mounted.
Example below. see also although
that example doesnt use a spare file.

[root at ostracod /scratch/media]# dd if=/dev/zero of=foo.img bs=1M
seek=1024 count=0
0+0 records in
0+0 records out
0 bytes transferred in 0.000066 secs (0 bytes/sec)
[root at ostracod /scratch/media]# ls -lh foo.img
-rw-r--r--  1 root  wheel   1.0G Jun 23 11:45 foo.img
[root at ostracod /scratch/media]# du -h foo.img
 48K    foo.img
[root at ostracod /scratch/media]# mdconfig -a -t vnode -f foo.img
[root at ostracod /scratch/media]# gpart create -s gpt md0
md0 created
[root at ostracod /scratch/media]# gpart add -t freebsd-ufs md0
md0p1 added
[root at ostracod /scratch/media]# newfs /dev/md0p1
/dev/md0p1: 1024.0MB (2097084 sectors) block size 16384, fragment size 2048
        using 6 cylinder groups of 183.72MB, 11758 blks, 23552 inodes.
super-block backups (for fsck -b #) at:
 160, 376416, 752672, 1128928, 1505184, 1881440
[root at ostracod /scratch/media]# !ls
ls -lh foo.img
-rw-r--r--  1 root  wheel   1.0G Jun 23 11:46 foo.img
[root at ostracod /scratch/media]# !du
du -h foo.img
736K    foo.img
[root at ostracod /scratch/media]# mount /dev/md0p1 /mnt/foo/
[root at ostracod /scratch/media]# df -h | grep foo
/dev/md0p1                  989M    4.0K    910M     0%    /mnt/foo
[root at ostracod /scratch/media]#

Hope this is helpful.
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