Management Of Backups With DAT Devices - Page 2

5 Dump the files to tape.

Once synchronized the servers on the local disk of the server connected to the DAT, we have to copy the data we are interested in, to a tape.

This guide aims to copy all the data on each copy. Possible other solution would be an incremental backup where, each day, we will copy only those files that have changed but I will not mention about that case here.

5.1 Periodicity

The proposal is to make a dump every day. This task will be automated using cron and we would have to put the tape in the DAT device once a day. The dump data to tape should be done after the servers synchronization, which, following this model, should be done once a day prior to dump data to tape.

In addition we will also copy a tape as monthly backup.

In short, we will have 5 + 12 tapes in a year, one for each working day of the week and one per month. The monthly tape will be on the first Monday of each month.

The process to run a cron on the first Monday of the month is not supported directly but is obtained as follows:

crontab -e
Add the following line:
50 10 1-7 * *  [ "$(date +\%a)" == "Mon" ] && /usr/local/bin/

This will launches the first Monday of each month, the script /usr/local/bin/ In the example of this guide, the only thing different that we will do the first Monday of the month is to put the 'monthly' tape. However, the script contains a reminder message for the person responsible for putting the tape which is sent via cron.

echo "Hi!"
echo "If I have been scripted well, today is the first Monday of the month"
echo "and you must to put the monthly backup tape."

5.2 Script

The following script will copy the data to tape from the directory where the files are synchronized from the original server

# Dump files to tape
# Variables
# Base dir to copy
# Logs dir
# Dir to copy
DIRS="serverA/var/log serverA/var/lib/mysql serverA/home/httpd"
# tape device
# Date format
FORMAT="[%Y/%m/%d %H:%M:%S]"
# End Variables
# Var for logs
DAY=`date --date='1 day ago' +%a`
MONTHDAY=`date --date='1 day ago' +%e`
# First Monday of the month?
if test  "$DAY" = "Mon" -a $MONTHDAY -ge 1 -a $MONTHDAY -le 7; then
          DAY=`date +%b`
date=`date "+$FORMAT"`
echo "----------------------" >> $LOGS/$DAY.log
echo "----------------------" >> $LOGS/$DAY.err
echo "$date" >> $LOGS/$DAY.err
echo "----------------------" >> $LOGS/$DAY.err
echo "Message from Backup Server."
echo "Below the summary of the nightly backup."
echo "$date Start backup" |tee -a $LOGS/$DAY.log
echo "$date Rewinding the tape..." |tee -a $LOGS/$DAY.log
mt -f /dev/$TAPE rewind
echo "$date Starting to copy" |tee -a $LOGS/$DAY.log
for dir in $DIRS; do
  date=`date "+$FORMAT"`
  echo "$date Started: $SOURCE/$dir" |tee  $LOGS/$dir.$DAY.log
  tar -vzcf /dev/n$TAPE -C $SOURCE $dir >> $LOGS/$dir.$DAY.log 2>>$LOGS/$DAY.err
  wait $!
  date=`date "+$FORMAT"`
  echo "$date Completed: $SOURCE/$dir" |tee -a $LOGS/$dir.$DAY.log
sleep 10
echo "$date Ejecting the tape..." |tee -a $LOGS/$DAY.log
mt -f /dev/$TAPE rewoffl
date=`date "+$FORMAT"`
echo "$date End backup" |tee -a $LOGS/$DAY.log

A little analysis to understand what the script does:
The servers are synchronized in this directory (see section "3 Synchronize the servers")
This is the directory where the script save a log about the operation.
DIRS="serverA/var/log serverA/var/lib/mysql serverA/home/httpd"
Within the directory defined in SOURCE, we choose what directories to save on tape. Each entry is separated by a space and being dumped to tape will create a brand (see Restoring files).
The tape device. In /dev there are two devices st0 and nst0. The first one, automatically rewind after each action. the second, ask for an explicit rewind. We wil use both of them that's why we reference the device in that way.
DAY=`date --date='1 day ago' +%a`
MONTHDAY=`date --date='1 day ago' +%e`

Variables used for "extracting" the backup log's names, for example.
tar -vzcf /dev/n$TAPE -C $SOURCE $dir >> $LOGS/$dir.$DAY.log 2>>$LOGS/$DAY.err
Is inside the loop which, for each directory, copy its contents to the tape in tar format and compressed (-z) in gzip format.

6 Restoring files

Restoring files is as follows:

  1. Enter the tape containing the files you want to restore in the DAT device.
  2. go at the point (record) of the tape containing the file you need. The tape is divided into as many points (records) as directories specified in the DIRS entry into the script.
    In the script the variable is:
    DIRS="serverA/var/log serverA/var/lib/mysql serverA/home/httpd"
    In this case, we have 3 records:
    1. serverA/var/log
    2. serverA/var/lib/mysql
    3. serverA/home/httpd
    To access a file that is under the first directory, simply rewind the tape:

    mt -f /dev/st0 rewind

    To access a file that is under the second directory:

    mt -f /dev/nst0 fsf 1

  3. Now, with the command:

    tar xvf /dev/nst0 serverA/var/log/[filename]

    for restoring a file, or

    tar xvf /dev/nst0 serverA/var/log

    for restoring all the directory log.

7 Summaries commands to use a tape device.

This small list shows only the most common options; however, it is highly recommended that you go through man pages of mt and tar command for more options/information. To use the following comands, you have to be root. Otherwise, you can use them with sudo.

Rewind tape drive:

mt -f /dev/st0 rewind

Backup directory /www and /home with tar command (z - compressed):

tar -czf /dev/st0 /www /home

Find out what block you are at with mt command:

mt -f /dev/st0 tell

Display list of files on tape drive:

tar -tzf /dev/st0

Restore /www directory:

cd /
mt -f /dev/st0 rewind
tar -xzf /dev/st0 www

Unload the tape:

mt -f /dev/st0 offline

Display status information about the tape unit:

mt -f /dev/st0 status

Erase the tape:

mt -f /dev/st0 erase

Goto previous record:

mt -f /dev/nst0 bsfm 1

Forward record:

mt -f /dev/nst0 fsf 1

Go to end of data:

mt -f /dev/nst0 eod

8 Conclusion

As always in this case, I can NOT assure that it works for everyone. I CAN assure, it works exactly in this way with my Ubuntu box for 16 months, now, without any big problems.
As I said at start, please, consider a starting guide to use a tape backup system.

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