I have a general purpose server which is running out of disk space. It currently has a RAID1 of two 2TB disks (WD RE4). So I'm going to buy two 4TB disks. I am considering the following options:
Make a RAID0 of the 2TB disks, then a RAID5 of the three 4TB volumes (two physical + 1 logical), for a total of 8TB
Leave the RAID1 array as it is, make another RAID1 of the 4TB disks, then a RAID0 of the two logical volumes (2TB + 4TB) for a total of 6TB (mdadm does not waste space with RAID0s made from different sizes);
Leave the RAID1 array as it is, make another RAID1 of the 4TB disks, then use LVM to combine everything into a 6TB volume group.
Is there a better solution I haven't thought of? Are there any obvious drawbacks or errors in the above options?
Edit: the server has many roles (web, ftp, nfs, database, gateway, etc), probably the heaviest I/O is made by the recordings of the security cameras. There are about 10 clients, divided among desktops, laptops and embedded devices. There is a backup NAS, but backups are not made exactly daily...