In December last year I decided to assemble my own dedicated little crunching machine. It had to fulfill certain criteria regarding power usage, noise level, and size within a limited budget. As a result of those criteria, I decided to go without an HDD and bought a cheap USB stick with USB 3.0 connectivity. Unfortunately Microsoft does not allow yet to install Windows on a USB stick so I had to go with Linux instead. As I also wanted to crunch CEP2 as well, although not exclusively, I somehow had to manage the disk writes to avoid trashing the new USB stick in no time. Because there are only limited capabilities to reduce disk writes through the BOINC software itself, I decided to use a RAM disk for the BOINC data directory instead.

So here comes an attempt in detailing what I did to create a RAM disk, to change the BOINC directory, to set up an backup routine and to get the RAM disk correctly started and stopped during the start-up and shutdown procedures of Linux. There are many ways to do it, this is just one way, I guess.

Starting point in my case:
- running Lubuntu 11.10 64-bit (any other Ubuntu derivative will do) properly installed on an USB stick (no Live mode)
- working and running BOINC 6.12.33 installed through Ubuntu packages
- an open terminal (CRTL+ALT+T)
- a healthy curiosity regarding linux and terminal commands

Create RAM disk and change data directory
1. Stop BOINC-client from running.

sudo service boinc-client stop

2. Create a directory as a mounting point for the RAM disk.
(Note: The default BOINC data directory was /var/lib/boinc-client )

sudo mkdir /var/lib/boinc-client-RAM

3. Mount a temporary file system (RAM disk) with the aforementioned directory as mounting point and check if you succeeded.
(Note: tmpfs is used over ramfs because it allows to set a fixed size of RAM and uses the swap file as safety. Use whatever size you want. In my case it was 65% of the RAM but absolute terms like 2000M are also possible.)

mount -t tmpfs -o size=65%,noatime none /var/lib/boinc-client-RAM
df -h

4. Copy data from current BOINC data directory into the new RAM disk data directory and check if you succeeded.

sudo cp -r /var/lib/boinc-client /var/lib/boinc-client-RAM
ls -l /var/lib/boinc-client-RAM

5. Change the owner of those files back to "boinc", remove writing rights for group and others and check if you succeeded.
(Note: The reason behind this is to 100 % mirror the original data-directory. Not sure if it is necessary, though.)

sudo chown -R boinc:boinc /var/lib/boinc-client-RAM
sudo chmod go-w /var/lib/boinc-client-RAM
ls -l /var/lib/boinc-client-RAM

6. Set-up Linux to create the RAM disk on start-up. You need to add a line to the file "fstab" in /etc/.
(Note: Change the line accordingly to what you have used in 3., don't forget to save with CRTL+O, and close with CRTL+X)

sudo nano /etc/fstab
Add the following line:
tmpfs   /var/lib/boinc-client-RAM   tmpfs    defaults,size=65%,noatime   0    0

7. Change the BOINC data directory to the new directory of the RAM disk. There are two files that need to be configured accordingly.
(Note: I am using my mounting point for the RAM disk, if you change that to another directory you have to change the lines accordingly.)

sudo nano /etc/default/boinc-client
Replace the line BOINC_DIR="var/lib/boinc-client" with:
BOINC_DIR="var/lib/boinc-client-RAM"

sudo nano /etc/init.d/boinc-client
Replace the line BOINC_DIR=/var/lib/boinc-client with:
BOINC_DIR=/var/lib/boinc-client-RAM 

8. Start the BOINC-client and check within BOINC-Manager through the messages function if the new data directory is used. It will say so in the beginning of the messages, approximately the 7th line which directory is used.

sudo service boinc-client start

Initialize/Terminate data directory during start-up/shutdown
As of now, if you restart your computer everything in the RAM disk will be lost and the BOINC-client will not start as it cannot find the files in the data directory, which of course is empty. So we need to create a backup-directory which will be used during shutdown to write everything from the RAM disk to the HDD (USB stick) and back at start-up.

9. Create backup directory and change the owner to "boinc".

sudo mkdir /var/lib/boinc-client-Backup
chown -R boinc:boinc /var/lib/boinc-client-Backup

10. Change the boinc-client service, so that it will copy everything to HDD when stopped and back to the RAM disk when started. For this we need to change the file "boinc-client" in /etc/init.d/
(Note: The boinc-client should be running, so that everything will be copied into the backup directory during the stop process, else the current RAM disk will be overwritten when the boinc-client service is started with the still empty backup directory. As an alternative you can make a manually backup by copying everything from the data directory into the backup directory.)

sudo nano /etc/init.d/boinc-client

Insert the following line into the start() function ahead of the line starting with "start-stop-daemon ..." and after "fi"
rsync -a /var/lib/boinc-client-Backup/ /var/lib/boinc-client-RAM/

Insert the following line into the stop() function ahead of "fi" and after the line "done"
rsync -a --delete /var/lib/boinc-client-RAM/ /var/lib/boinc-client-Backup/

Don't forget to save, with CRTL+O and close with CRTL+X. 

Automatic Backup
As of now, every time someone stops or starts the service "boinc-client" the content of the RAM disk will be copied to the HDD (USB stick) or to the RAM disk. This happens automatically if you start or shutdown your linux and manually if you use "sudo service boinc-client start/stop". The only thing missing is an automatic backup after every X hours in case of an power/system failure. For this I use crontab.

11. Create a task that will take a backup every X hours, using "crontab".
(Note: In my case, it will only take a backup at 6 o'clock in the morning everyday to minimize disk usage on the usb stick. Every two hours for example would be 0 */2 * * * /usr/...
Furthermore it is mandatory to finish the last line with a RETURN key, especially if only one line is inserted, to create a blank line at the end of the file. Don't use blank lines between job entries, only for the last job. )

sudo crontab -e

Add the following line and confirm with a RETURN key to insert the blank line:
0 6 * * * /usr/bin/rsync -a --delete /var/lib/boinc-client-RAM/ /var/lib/blinc-client-Backup/
(blank line)

12. To minimize the probability of losing finished WUs which have not yet reported to WCG, BOINC can be adjusted to report immediately by changing the cc_config.xml file.
(Note: Having BOINC connect every hour might work as well, but I have not tested it.)

sudo nano /etc/boinc-client/cc_config.xml
Change or Add the following line within the option tag. 
<report_results_immediately>1</report_results_immediately>

Note
That should be everything, I hope. Be careful, double check and experiment with the code. I cannot guarantee that everything is spelled correctly, done in the right order or even explained correctly. A native speaker will have surely realized that I am not one of them, although I have tried to be as accurate as possible, I never will be.