[zfs-discuss] Testing an application and using rollbacks.

Alessandro MACUZ alessandro.macuz at gmail.com
Fri Oct 25 14:13:13 EDT 2013


I'm testing the power of rollbacks but it seems I don't get them work.

Foreward

The dataset is a zvol exported via iSCSI to a VMguest.
As test I chose emacs as the wonderful application I want to install on my
system but for which I didn't know if the installation would be successful
or not.

I tried two scenarios, since I was not convinced that via the first attempt
I did things correctly.

First attempt

1) with the OS live I took a snapshot (@before-installing emacs);
2) I installed emacs (on Debian wheezy) and verified it was there (call me
picky but I did it);
3) with the OS live I took a snapshot (@after-installing emacs);
4) I shutdown the VMguest;
5) zfs rollback -r <dataset name>@before-installing emacs;
6) Powered on the VMguest;

Emacs was shown as installed, I expected it not to be installed.

I destroyed the two snapshots and I uninstalled emacs

Then the second attempt (snapshots taken with VMguest shut down)

1) I shut the VMguest down;
2) I took a snapshot (@before-installing emacs);
3) I installed emacs (on Debian wheezy) and verified it was there;
4) I shut the VMguest down;
5) I took a snapshot (@after-installing emacs);
6) I powered up the VMguest;
7) I checked emacs was there (obviously);
8) I shut the machine down;
9) zfs rollback -r <dataset name>@before-installing emacs;
10) Powered on the VMguest;

Emacs was shown as installed, I expected it not to be installed.

Where am I wrong in my procedure?

P.S.
Honestly I believe that if I have to rollback to a snapshot to a point in
time before trying a change on a filesystem that snapshot must represent an
unmounted filesystem.

That's why I ran the second attempt, but I didn't get the results I
expected.

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