I have an Eee ASUS which comes with two ssd disks
I have installed Ubuntu 9.04 in the small one (8 Gb) but I keep the big one (30 Gb) empty, formatted in ext3 under/dev/sdb.
Could it be possible to dedicate this device to the/usr/local?
Is it possible or feasible to split the filesystem between two different physical disks and runing smoothly(eg one with the /,/etc/, /bin, /sbin .. and the other with the /home, /usr, /lib)?
It's easier to set this up at install to save having to mess around in the scary/etc/fstab.
Fstab can make things go badly wrong very easily if you don't know exactly what you are doing. I would advise having an Ubuntu (or any other linux distro's) Cd easily at hand ready to boot up into a LiveCd session via the "Try Ubuntu without making changes to this machine" option. If you don't want to try a sneaky reinstall the i would recommend backing up fstab as follows. On a command line
Applications - Accessories - Terminal
sudo cp fstab fstab.060809
Note the "ls" is a lower-case "LS" and the "sudo" command will ask you for your normal user password, not your SuperUser/Root one. While "ls" shows a list of what's in the folder there's quite a lot in /etc so i think it's better just to look for specifically what we want to see. You may notice that the first time you do "ls fstab.*" it shows nothing but the 2nd time it shows the new file you've just created with the CoPy command. Some background notes on my suggestions ...
To maximize performance of your system and to make it very robust i would recommend keeping things as simple as possible. I would recommend partitioning your drives like this, assuming that the smaller 8Gb drive is recognized as sda and that the larger 30Gb one is sdb
sda1 8Gb Primary Partition of file-system = ext3 to be set to "Mount Point" = /
sdb1 20Gb Primary Partition of file-system = ext3 to be set to "Mount Point" = /home
sdb2 5Gb Primary Partition of 'file-system' = linux-swap, this doesn't need a "Mount Point"
sdb3 5Gb(ish) Primary Partition of file-system = ext3 also with no "Mount Point"
Note that sdb3 is for having fun installing other versions of linux and generally experimenting with - safely away from your main install. The linux-swap on sdb2 needs to be at least equal to your ram size but a little more is wise, more than twice your ram size is excessive & wasteful unless you plan to upgrade ram anytime soon. If it needs to be larger than 5Gb then take that from sdb3 rather than sdb1. Plenty of versions of linux fit into even 1Gb or less but having 5Gb means you can test out ideas for a bigger distro such as Ubuntu.
https://help.ubuntu.com/community/SwapFaq The /home is where all your data&settings are kept so having it on a separate partition from the OS means you can reinstall your OS, or even a completely different one without damaging you data. While there can sometimes be small performance increases by splitting other folders off to different drives i really don't think that's relevant to ssd drives as they don't have a read/write head bouncing around between different folders. There's some theoretical potential for a tiny improvement by getting a very expensive tiny fast normal sata drive but i really wouldn't recommend making things that complex without a lot more linux experience.
The "Mount Points" get defined either in the installer or in fstab and such, easiest to do this in the installer but i do have a trick for doing this without necessarily losing all your data and programs in the process.
Please let us know whether you want my neat trick or would prefer links to dealing with the scary fstab. I could give both if you want to compare. Also please let us know what your ram size is in case there's a surprise that requires a re-think about the layout.