I have two HDD. I am running korora FC20.

1. dev/sdb : 74 gb
2. dev/sda : 500 gb

The boot loader, the home folder and evolution is in SDB. Now the problem is due to heavy emails in evolution, the drive is overloaded and throwing error of low disk space.

I have to either shift the evolution or let the machine boot from
to SDA to solve the problem.....

Please let me know how to do it....I need your help...
Thanks in advance...

my suggestion, no need to change boot option,
i assumed your mail in /var

then just move /var to sda after that make symlink for var at /

or another way round is use usermode change your $HOME place in sda if your mail in your $HOME

hope you get idea with this

where is your /home? probably you can move that too.

Here is my evolution

/home/emfex/.local/share/evolution

My home is in dev/sdb. This is the smaller volume...

I would love to do any of these suggestion.
Kindly let me know in steps...Please...
I am a newbie...

yes, you can
1. create a dir in /dev/sda, move your /home/emfex/.local/share/evolution onto that dir and create a link from the original location
2. create a dir in /dev/sda and move your home
but first you need to find which dir causes the trouble, you can use the command du -sh <dir> to check the size

ok the step ,

show us the output of below command

# df -h

then easy for us to tell the step

What I have done is listed ...

1. Take a back up of Evolution to SDA
2. My other important files were already in SDA
3. Executed the following command. SDA is already mounted as home2.

# usermod -m -d /home2/emfex emfex

4. it creates the new home at sda. (It should also copy the files of old home to new home but it did not copy anything...!!! God knows why...!!!)
5. reboot the machine.
6. restore the evolution back up
7. Everything is working fine...

Thanks for all your supports and ideas....
You people are rocking... !!!

glad to know its working and thank for posting back the solved issue