Source: https://www.baadnwz.eu/search/label/tutorials

Although there is a2sd, that keeps the apks on the sd-ext some files are stored on phone's nand on /data partition and if we install alot of apk's then you remain out of free space. WE DO ALL THIS WITH PHONEON, NOT IN RECOVERY 1st let's see how much free space i'm having:

# df -h | grep data

/dev/block/mtdblock5 147.6M 76.7M 70.9M 52% /data

As you can see i have left about 70 MB free. Let’s see what folders eat my space:

#du -sk /data/data/* | sort -rn | head

18641 /data/data/com.navngo.igo.javaclient

14911 /data/data/com.opera.browser

6756 /data/data/com.google.android.gm

5194 /data/data/com.android.providers.contacts

3661 /data/data/com.htc.launcher

3083 /data/data/com.htc.googlereader

1276 /data/data/com.swype.android.inputmethod

1172 /data/data/com.android.settings

1144 /data/data/com.htc.android.mail

1084 /data/data/and.blogger

Ok so it seems that iGO and Opera is eating 32 megs together. I'll leave data/data/com.google.android.gm alone since it's gmail and I want to be more responsive by keeping its files to nand(i only have a class 4 card). Lets get to work. 1st we need to make a folder on sd-ext where to keep the files.

#mkdir /system/sd/.moreapps

I made the folder .moreapps. Now let's move stuff and symlink them.

First we move them:

#mv /data/data/com.navngo.igo.javaclient /system/sd/.moreapps/com.navngo.igo.javaclient

Then we symlink them: #ln -s /system/sd/.moreapps/com.navngo.igo.javaclient /data/data/com.navngo.igo.javaclient

#

Now we repeat the operation for opera:

Move:

#mv /data/data/com.opera.browser /system/sd/.moreapps/com.opera.browser

Symlink:

ln -s /system/sd/.moreapps/com.opera.browser /data/data/com.opera.browser

Now let's check again my free space.

#df -h | grep data

/dev/block/mtdblock5 147.6M 51.8M 95.9M 35% /data

Well it seems to me I gained 35 mB without uninstalling apps, without moving ALL of them to SD and experience some lags.

Now let's check if we made the symlinking right

#ls -al --color=none /data/data/com.opera.browser

lrwxrwxrwx 1 0 0 38 Feb 22 05:46 /data/data/com.opera.browser -> /system/sd/.moreapps/com.opera.browser

Yap all seems right. Opera and iGO are working at same speed, i freed up some space. Everyone's happy. The advantage of this method is that you can choose what to move to sd-ext you don't have to have all to sd-ext. Now make sure you don't name your folder in /system/sd "data" since a2sd script will move back on nand all its contents. This method is recommend for GPS software, Browsers, Games, some apps you got from market. It's best to  leave system apps there to avoid FCs or slowdowns. If anything goes wrong with your app after this you can always move them back. 1st you delete the symlink (rm /data/data/whatevar) then move it back