Thursday, 10 October 2013

My first Raspberry Pi - day 3

External disc drive setup

I need to attach a decent size disc drive to my Pi to store radio recordings from my PVR. It will also allow me to create files, and use swap space, without worrying about wearing out the SD card. Given that I'm using a disc drive, it makes sense to put all the Pi's software on it, relegating the SD card to a "bootloader".

I found a useful guide to running a Pi from an external disc drive on I've done things a bit differently, of course...

Firstly, I created four partitions: 2 of 8GB for "system" and "spare", 2GB swap and the remainder of the disc (about 212GB) for "home". Then I created and enabled the swap space, then formatted the other partitions:
fdisk /dev/sda
mkswap /dev/sda3
swapon /dev/sda3
mkfs.ext4 /dev/sda1
mkfs.ext4 /dev/sda2
mkfs.ext4 /dev/sda4
The next stage is to copy everything needed from the SD card, and create other directories and mount points:
mkdir /mnt/system
mount /dev/sda1 /mnt/system
cd /mnt/system
rsync -av /{bin,etc,lib,opt,root,sbin,selinux,srv,usr,var} .
mkdir boot dev home media mnt proc run spare sys tmp

mkdir /mnt/home
mount /dev/sda4 /mnt/home
cd /mnt/home
rsync -av /home/* .
Finally, edit /boot/cmdline.txt and /mnt/system/etc/fstab:
dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/sda1 rootfstype=ext4 elevator=deadline rootwait

proc            /proc           proc    defaults          0       0
/dev/mmcblk0p1  /boot           vfat    defaults,ro       0       2
/dev/sda1       /               ext4    defaults,noatime  0       1
/dev/sda2       /spare          ext4    defaults,noatime  0       1
/dev/sda3       none            swap    sw                0       0
/dev/sda4       /home           ext4    defaults,noatime  0       1
On reboot, check that everything's mounted as expected:
root@firefly:~# df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs          7.9G  2.0G  5.6G  27% /
/dev/root       7.9G  2.0G  5.6G  27% /
devtmpfs        235M     0  235M   0% /dev
tmpfs            49M  264K   49M   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           507M     0  507M   0% /run/shm
/dev/mmcblk0p1   56M   19M   38M  33% /boot
/dev/sda2       7.9G  146M  7.4G   2% /spare
/dev/sda4       212G  190M  201G   1% /home
root@firefly:~# free -h
             total       used       free     shared    buffers     cached
Mem:          485M        59M       426M         0B       6.2M        27M
-/+ buffers/cache:        25M       460M
Swap:         2.0G         0B       2.0G

Make /tmp a ramdisc

For optimum performance it's nice to have /tmp in memory instead of being written to disc. With a large swap partition I needn't worry about running out of memory. If /tmp begins to fill up its least used files will be swapped out, leaving the active ones in memory.

All this requires is one extra line in /etc/fstab:
tmpfs           /tmp            tmpfs   size=256M         0       0

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