UFS Resulting size of snapshot file

[Cedric62]

Well, to make a long story short, below is the result of gpart show on my system.

root@Asus:~ # gpart show
=>        40  1953525088  ada1  GPT  (932G)
          40   964689920     1  freebsd-ufs  (460G)
   964689960     8192000     2  freebsd-swap  (3.9G)
   972881960   980643168     3  freebsd-ufs  (468G)

=>        40  1953525088  ada0  GPT  (932G)
          40      532480     1  efi  (260M)
      532520  1945624568     2  freebsd-ufs  (928G)
  1946157088     7368040     3  freebsd-swap  (3.5G)

According to the below information only a tiny percentage of the available space within my root partition (ada0p2) is actually being used at the moment.

root@Asus:~ # df -h
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ada0p2    899G     26G    801G     3%    /
devfs          1.0K      0B    1.0K     0%    /dev
/dev/ada0p1    256M    1.3M    255M     0%    /boot/efi
/dev/ada1p1    446G     25G    384G     6%    /diskbkp
/dev/ada1p3    453G    135G    282G    32%    /diskdoc
linprocfs      8.0K      0B    8.0K     0%    /compat/linux/proc
linsysfs       8.0K      0B    8.0K     0%    /compat/linux/sys
devfs          1.0K      0B    1.0K     0%    /compat/linux/dev
fdescfs        1.0K      0B    1.0K     0%    /compat/linux/dev/fd
tmpfs          8.9G    4.0K    8.9G     0%    /compat/linux/dev/shm

So, it appears that I'm only using 26 gigabytes out of the available 899 gigabytes within my root partition, so based upon this information, I decided to try and use the below command to create a snapshot of my root partition, and to store that snapshot onto my second hard drive, (ada1).

mksnap_ffs / /diskbkp/snapshot021526/root021526.snap

The above command seemed to execute successfully, but it only took a few seconds to carry out its process, and in the end, I ended up with a snapshot file which is only 140 megabytes in size. See below.

So, my question is, does the above file I created actually contain copies of files, which I could the use to potentially restore my system after a disaster, or does the snapshot file contain something else entirely?

Also, I opted to go with the UFS option because I'm not sure if my system has enough ram to adequately support ZFS, and the two hard drives I have installed in my desktop machine are a little bit on the creaky side, and I don't know if using ZFS and mirroring on these drives is a wise idea. Also, I would like to learn more before I try something like that.

 

[homeadm]

The above command seemed to execute successfully, but it only took a few seconds to carry out its process, and in the end, I ended up with a snapshot file which is only 140 megabytes in size.

So, my question is, does the above file I created actually contain copies of files

Snapshot tracks changes made to source volume. Therefore, it's initially small. It will gradually grow as you copy/delete/edit more files.

which I could the use to potentially restore my system after a disaster

Partially. A snapshot is used to undo changes to the volume since creation of the snapshot. If something goes really south, only backup will help.

 

[Cedric62]

If something goes really south, only backup will help

I'm pretty good at making things go really south, so I guess I'd better be careful until I'm certain that I have reliable method of recovery.

Actually, I haven't tried using "pkg upgrade" yet, but I understand that mishaps can sometimes occur after issuing this command. If the snapshot I created isn't completely helpful, then I suppose that I can do a fresh reinstall, and then use "rsync" to restore all of my settings. I recently tried using rsync after doing a fresh reinstall, and it seemed to work, once I used the correct flags with rsync. So, at least I'm not completely without a safety net.