I'd just get the 8-bay if you don't want to bother with expansion later. Either box will work the same.
I've not had a card fail, nor switched my card to a new machine, but with the battery backup unit (BBU) attached, I would expect the card to remember the settings if you moved it into a new machine, granted it's all set up the same way. That being said, I would NOT trust it to work so easily. Better to back up the data on the RAID and just set up a new one on a new machine, then copy the data back over after tests verify it's all working properly.
If the card failed, I'd assume the data on the RAID would be lost, but again, RAID is not backup, so you need to back up this data and forget about what-if. It's more likely that your house is robbed, burns down or destroyed by earthquake, and your data is all gone anyway, unless you keep backups outside your home. (A good idea for über-critical data.)
My disks are WD2003FYYS (2TB) and WD4000FYYZ (4TB). I'll repeat that you need enterprise disks in a RAID like this. I've read plenty of complaints from people that used standard disks and had failures. They don't need to be SAS or 10,000rpm, but they do need to be designed for RAID use.
About speed. This setup will be easily 10x faster than Firewire. If you put eight of the WD2003FYYS HDDs in RAID 6 with the Areca and TR8X, you'll see speeds of about 816MB/sec write, and 715MB/sec read. If you use faster disks, such as the 4TB WD4000FYYZ, you'll see speeds even faster. If you use SSDs, then much faster. It's all about money!
I've not had a card fail, nor switched my card to a new machine, but with the battery backup unit (BBU) attached, I would expect the card to remember the settings if you moved it into a new machine, granted it's all set up the same way. That being said, I would NOT trust it to work so easily. Better to back up the data on the RAID and just set up a new one on a new machine, then copy the data back over after tests verify it's all working properly.
If the card failed, I'd assume the data on the RAID would be lost, but again, RAID is not backup, so you need to back up this data and forget about what-if. It's more likely that your house is robbed, burns down or destroyed by earthquake, and your data is all gone anyway, unless you keep backups outside your home. (A good idea for über-critical data.)
My disks are WD2003FYYS (2TB) and WD4000FYYZ (4TB). I'll repeat that you need enterprise disks in a RAID like this. I've read plenty of complaints from people that used standard disks and had failures. They don't need to be SAS or 10,000rpm, but they do need to be designed for RAID use.
About speed. This setup will be easily 10x faster than Firewire. If you put eight of the WD2003FYYS HDDs in RAID 6 with the Areca and TR8X, you'll see speeds of about 816MB/sec write, and 715MB/sec read. If you use faster disks, such as the 4TB WD4000FYYZ, you'll see speeds even faster. If you use SSDs, then much faster. It's all about money!