There are also specialized filesystems that support this as well without LVM: Btrfs, and ZFS to name a couple.
btrfs is still on-development and AFAIK features such as RAID / multi-drive isn't fully stable yet.
If your drives are so small that you need two to fit the entire blockchain, perhaps you should consider simply getting a larger one. A cheap ($18) 250g drive should fit the blockchain now, but give it some room for the future: you can get a
500g drive for $20...
Or just use pruned mode if you don't need past transaction/blocks information. Besides HDD with small capacity have lower price/space ratio, you can get 4TB HDD for $100 which have price $0.025/GB while the one you mentioned have price $0.04/GB.