I'm building a NAS, based on the Intel SS4200
. There are 4 drive bays in the machine for use with SATA disks, two of which I plan on filling now, the other two which I plan on filling later. The box also includes an IDE connector to which I will connect an 8GB Disk on Module
onto which I will install Slackware.
I wish to have all drives in the box show up as one contiguous volume. What partitioning/LVM/RAID configuration can I use which will allow me to:
1. Add a disk and transparently grow the available space of the volume?
2. Replace a disk with a larger disk and transparently grow the available space of the volume?
3. Lose a disk to hardware failure and replace it with a new one with no data loss?
If I use RAID 5, I'm pretty certain I can get numbers 1 and 3 above, but I'm not sure about number 2. The downside is that I'd have to start with 3 disks in the machine, and I'm unsure if adding a 4th disk whose size is larger than each of the 3 starting disks would lead to wasted space. For instance, if I start with three 1TB drives in RAID 5, and then add a 2TB 4th drive, would my available size go from 2TB to 3TB? Or from 2TB to 3.xTB? Is it important in a RAID 5 setup to have all disks the same size?
With LVM, I can certainly get number 1 above, but what about 2 and 3? I know you can use LVM to present many disks or partitions as one contiguous volume, but if I have two 1TB drives in one volume, and only have 300GB of data, then would the second drive remain empty until I broke the 1TB barrier? In this case, it's wasted space from the get go.
I suppose another option would be to start with RAID 1 until I can afford a third disk. When adding the new disk, could I switch to RAID 5 without data loss?
I'm planning on maintaining a full mirror of the NAS on some USB disks as a backup, so if configuration changes to the NAS require wiping the disks and restoring from backup, it's not a total loss. However, it certainly makes me nervous to be in a state where only one copy of the data exists, so I'd rather find a solution where I can add and upgrade disks in the NAS without relying on the backup copies.
Any insight/experience you can share would be greatly appreciated!