Prevent lots of writes on Ubuntu Server running from flash drive

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http://unix.stackexchange.com – I would like to have a setting, where Ubuntu Server is installed and booting from a flash drive (SanDisk Cruzer Fit 8GB), with two HDDs running in RAID1 and 4 drives running with RAID0 (only 1 drive at the beginning and adding up more over time). All drives, except for the pen drive should be encrypted and decrypted when booting up the system, thus, unplugging the pen drive would render the whole system useless. There should be a backup of the pen drive somewhere, just in case the pen drive burns down. All HDDs should run LVM2. All the writing of files should be on the HDD and only on very r (HowTos)