running a tar command eats all resources

I am running a Rails application on my ubuntu 12.04 server. I have set up a cron job to take backup of all files uploaded to my application every morning at 2 am. It is a lot of files (around 900 mb). But when the users has to use the app later in the morning they can access it. So I logged in with SSH (which goes incredible slow) when finally in I run a top command and sees that gzip process is filling up all top 10. They are quite small but i suspect there is even more of them.

This is the tar command that gets executed

tar -cvzf $BASEBACKUP/uploads-$DATE.tar.gz /var/www/bptrial/current/public/uploads/* --exclude=tmp

My crontab

* 2 * * * cd /home/user/backup && sh mysql_backup.sh && sh files_backup.sh  >> /tmp/cron.log

Should really take so many hours to zip 900mb of files? And why does it have to eat all the resources?

Solution 1:

I think fkraiem is correct.
To elaborate:

According to the crontab man pages

user@host $ man 5 crontab 

The time and date fields are:

          field          allowed values
          -----          --------------
          minute         0-59
          hour           0-23
          day of month   1-31
          month          1-12 (or names, see below)
          day of week    0-7 (0 or 7 is Sun, or use names)

   A field may be an asterisk (*), which always stands for ``first-last''.

In your command

#m h  dom mon dow   command  
 * 2   *   *   *    cd /home/user/backup...  

You're saying, EVERY minute of hour 2 of every day of every month of every day of week. In other words, every minute of 2am will start another instance of your given command.