samba_backup error and restoring old backup files

[elyad alaei]

Hi
Some months ago, we have installed samba 4.0.3 on ubuntu 12.04 LTS as our
only domain controller and started to join our client computers (about 100
PCs) and defining our users (about 200).
After a while, we have upgraded it to 4.0.10 as mentioned in "Upgrading a
source version" in samba4 howto.

To backup the samba database, I stop samba service at 2:00 AM every night
and backup using samba_backup script and re-run samba4 service with the
help of crontab. It could always create "samba4_private" file but "sysvol"
and "etc" files were not created in some days! (I didn't pay attention to
this issue because it backed up both "etc" and "sysvol" each 2 or 3 days or
sometimes everyday!)

Today we saw some malfunctioning and the command:
#service samba4 stop
gives the error: <<samba4: unrecognized service>> but the output of command:
#initctl list | grep "sam*"
is correct : <<samba4 start/running, process 18966>>

When I checked backedup files, I saw the latest backup of "sysvol" and
"etc" is back to 31 DEC 2013! but "samba4_private" are all backed up till
now.
To stop samba, I removed samba4.conf from /etc/init and restarted the
server and then run the samba_backup script! unfortunatly it doesn't create
"sysvol" and "etc" backup files and writes these errors on the screen:

root at smb4srv:/home/adminit# /usr/sbin/samba_backup

Failed to insert into
./private/sam.ldb.d/DC=DOMAINDNSZONES,DC=IT,DC=TUB.ldb.bak.tmp

failed to copy ./private/sam.ldb.d/DC=DOMAINDNSZONES,DC=IT,DC=TUB.ldb

Error while backuping
./private/sam.ldb.d/DC=DOMAINDNSZONES,DC=IT,DC=TUB.ldb

Please note that, despite we get these errors, the "samba4_private" file is
created each time I run samba_backup! but I don't know whether it is
corrupt or not.
Now my questions are:
1.How can I know whether "samba4_private" is corrupt or not.
2.What if I restore (abit old) backup files of 31 DEC 2013?! Can it couse
any malfunctioning in our existing clients?!
3.How can I mix old "sysvol" and "etc" backup files with latest
"samba4_private" if it is not curropt?!

Tanx