Confusion about DAS and eSATA

[Boomslang]

Hello, I'm shopping around to replace an aging NAS system. I like what I've been reading about eSATA (6.0Gb/s) and DAS-type setups. However, I'm unclear about some things.

I would basically like to build a small 8-disk box with hardware or software RAID, and then hook it up to a desktop PC over eSATA. I know that things like this exist - for example, http://www.cwol.com/serial-ata/5-bay-raid-enclosure-quad-t5r5esuf.htm is sort of what I am looking to build.

Is this thing running a full (embedded) OS? I know my way around Linux and embedded OSes, and if it is, I am confident I could build something similar. However, that brings me to the next question - how does eSATA work in this case?

My understanding was that a HBA with eSATA (or SFF-8088) could be installed on the host PC, and from there you can use a port multiplier to attach drives. Management of the drives would be done by the host PC. In the case of the machine I linked to (that would seem to be running its own OS), what happens when you connect to the eSATA port of that machine using an eSATA port on my desktop machine? It's like connecting two PCs together over eSATA, isn't it? What is the result?

Also, hypothetically, if I had an eSATA HBA with dual ports, what would happen if I plugged two of the machines I linked above into the same PC? Could I transfer data between them at full SATA speed (assuming my disks could keep up)?

Thanks for helping clear things up for me.

 

[pjkenned]

Odds are, you want a HBA with SFF-8088 connectors (converting them from SFF-8087 costs enough that it's worth just getting external ports). You then buy two SFF-8088 cables, an external enclosure (with power supply), a two port SFF-8088 to SFF-8087 converter, and two SFF-8087 breakout cables and you are set.

The cheap way to do this is using non-hot-swap bays in the enclosure but at 8 drives you will start to want hotswap sooner or later. Add in 3x 3-in-2, or two 4 (or 5) in 3 hot swap bays and you are set.

As for the HBA's, I would recommend an Areca 1680X, Adaptec 3085 or 5085.

If you wanted to do this really inexpensively, you could get two eSATA expanders/ port multipliers for about $50 each instead of the HBA's and use two eSATA connectors on your motherboard, on a cheap HBA, or convert tow internal SATA ports to eSATA, but you will be limited to 1.5 or 3.0gbps max for every 4-5 drives, and you won't have hardware raid.

If you wanted a linux/ FreeBSD machine running software raid, then you may as well set up iSCSI and just do the access over a gigabit network (using multiple NIC's if required).

 

[Boomslang]

So if I wanted a hardware RAID array connected with eSATA or SFF-8088 I would need the RAID-enabled HBA to be installed on my host PC - that makes sense to me. That would mean that if I wanted to disconnect it and hook it up to another PC, I would need to move the HBA along with it to keep the RAID intact.

But what about those prebuilt RAID DASes like the one in the link? It would seem that you can just connect it to any PC with an eSATA port and enjoy the benefits of DAS with hardware RAID and portability between any PC with eSATA without having to keep it tethered to a HBA. Is this inaccurate?

Thanks for the help so far.

EDIT: To clarify - I would like to build a storage target that manages its own RAID array, and I would like to be able to plug this machine into any PC with eSATA (or SFF-8088, no preference) and have it appear as a single large disk.