So how good it's performance with single port eSATA enclosures?
Going to need a significant amount of storage soon. eSATA it's significantly cheaper than a SAS enclosure + card.
I had thought that if i'm going to use a snapraid setup for these drives (to make it so only one drive it's active for any given opperation, it should work the same.
If it is an enclosure with just 1 hard drive then it will probably work fine. If you are looking at an eSATA enclosure with multiple hard drives then it probably has a SATA port multiplier inside. SATA port multipliers require specific port multiplier support from the main SATA controller in your PC. As far as I know none of the Intel or AMD SATA controllers on a motherboard support port multipliers. You have to use another PCIE SATA card with support for that. My experience with them 10 years ago is that they are all flaky and will suffer from random disconnects and dropouts.
USB3 is far more popular now and basically killed eSATA. USB can also have problems with random disconnects.
How many drives do you need in the external enclosure? Commerically available SAS enclosures are expensive. If you have an old PC case and power supply you can make that into a SAS enclosure with a few cables and adapters
This would be the route I'd take if I were in your shoes, OP. Basically a DIY DAS (direct attach storage). If you have an old case + PSU, all you'd really need is the LSI card, which can be had for roughly $35 on eBay, and some cheap cables.
Alternatively, upgrade your current case to one that can support more drives and do it all in one case. You'd still need the LSI card and some cables, maybe a 1 to 4 SATA power splitter or two for the additional drives.
What are you asking about? Are you looking to use SAS drives through eSATA? While SAS drives support connection though SATA, your controller needs to be SAS compatible. You can't just use any SATA enclosure with eSATA or USB.
Standalone external SAS enclosures are expensive is because of lack of supply and demand. A klunge may be to use an internal multi-drive 5.25" bay dock and use it outside your PC case, running the SAS/SATA and power cables out the back of your PC. I tried this with a 4 bay dock that happens to support SAS drives and has SATA only connectors on the back. I'm not sure if it was the dock or the cables, but it only worked intermittently. If the drives were connected directly with SAS cables, they were fine.
So the idea that there's no demand for this just can not be true, since people are literally making the hardware, just not the piece of metal to wrap around the drive cage so you can set it on a desk.
USB is even cheaper and far easier to find these days.
Snapraid is only for parity. If you intend to pool up your storage you need something else like mergerFS on top of it. But if you care about performance it is not really a great option.