Now that I got a little time to work on my Raspberry Pi, I decided to have 2 2GB flash drives mounted at boot to save some write cycles on the SD card:
After a few failed times, I googled for a while and the important bit is the 6th field in your /etc/fstab file. Here's mine:
[root@pi ~]# cat /etc/fstab
#
# /etc/fstab: static file system information
#
# <file system> <dir> <type> <options> <dump> <pass>
devpts /dev/pts devpts defaults 0 0
shm /dev/shm tmpfs nodev,nosuid 0 0
/dev/mmcblk0p1 /boot vfat defaults 0 0
/dev/sda1 /var ext4 defaults 0 2
/dev/sda2 /data ext4 defaults 0 2
/dev/sda3 /tmp ext4 defaults 0 2
/dev/sdb1 /home ext4 defaults 0 2
The "2" in the 6th field tells the kernel to wait for the drive to be available before trying to mount it.
Here's the "mount" command output:
/dev/mmcblk0p1 on /boot type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=cp437,iocharset=ascii,shortname=mixed,errors=remount-ro)
/dev/sdb1 on /home type ext4 (rw,relatime,user_xattr,barrier=1,data=ordered)
/dev/sda2 on /data type ext4 (rw,relatime,user_xattr,barrier=1,data=ordered)
/dev/sda3 on /tmp type ext4 (rw,relatime,user_xattr,barrier=1,data=ordered)
/dev/sda1 on /var type ext4 (rw,relatime,user_xattr,barrier=1,data=ordered)