Multiple RAID selection on a single 16-port adapter

There's a few reasons you might see a minor performance drop by having multiple RAID arrays - firstly you're likely to be splitting the cache to some degree but that shouldn't be particularly impacting. You're also more likely to introduce queue/bus contention but again that shouldn't make much of a difference. What will have a bigger impact is that you'll have less disks in the actual array which is likely to have a much bigger impact overall.

You're not going to see any difference with RAID-10. With RAID-5 and RAID-6 you might theoretically see an indiscernibly small difference in write throughput when writing heavily to both LUNs at the same time, depending on Areca's implementation. What you're concerned with is essentially premature optimization, and you should probably be focusing on these general rules instead before you turn to vendor-specific implementation quirks:

• Make sure your write-through cache is functioning properly. A good write-through cache accounts for a huge amount of your write performance, especially with random writes, in striping with parity.
• Understand partition alignment. I believe that on Linux, most of the graphical partition tools (e.g. GParted) will align your partitions by default, but fdisk and parted won't. This leads to boundary crossings, which kill your performance by potentially turning a single write operation into several reads and several writes.
• When you write in RAID-5 or RAID-6, the controller needs to read data from the entire stripe in order to recompute parity. Understand the implications of segment sizing and how it relates to your data, especially in terms of partial writes (which require reads before a portion of the block can be modified). In general, the larger your stripe width, the greater your sequential read throughput, but the more data that needs to be read when recomputing parity on write. The smaller your stripe width, the better the possibility that you aren't making partial writes, and don't need to recompute parity at all, but the more disks you need to fulfill I/O requests. It's a trade-off and you really need to understand your application.
• Listen to your vendor's recommendations regarding application performance. Areca allows you to create multiple RAID arrays in a volume set -- take advantage of this functionality if your applications demand I/O performance. You can create multiple RAID volumes with different stripe widths.

I've used a number of older 11xx and 12xx series Areca controllers and currently manage a server with a 1880 series controller.

The way Volume management works with Areca cards is similar to how LVM works on Linux. First you assign drives to RAID Sets which are similar to Volume Groups. Then you create Volumes on the RAID Set and it's at the Volume level that you specify the RAID level. Hot Spares can be Global or tied to a particular RAID Set. But you can mix RAID levels on a single RAID set if you wish. They also support online raid level and volume migrations.

The performance impact of having multiple volumes on one RAID SET is going to depend on your workload and a number of other factors like system ram, controller cache etc. But keep in mind that most of the Areca controllers use standard memory modules for cache so they are field upgradeable. I just checked and it looks like the 1260 uses so-DIMMS but I didn't look to see what the largest size so-dimm it can accept.