Offtopic: hardware advice for SAS RAID6

On the heels of last week's post asking about hardware recommendations, I'd like to ask a few questions too. :)

I'm considering my first SAS purchase. I'm planning to build a software RAID6 array using a SAS JBOD attached to a linux box. I haven't decided on any of the hardware specifics.

I'm leaning toward this PCI express LSI 3801e controller:
http://www.lsi.com/storage_home/products_home/host_bus_adapters/sas_hbas/lsisas3801e/index.html

Although, Adaptec has a similar PCI-X model.

I'd probably purchase a cheap Dell rackmount 1U server (e.g. PowerEdge
860) for the controller. It has dual Gb ethernet, which I'd channel bond for decent network I/O performance.

The JBOD would ideally be 1U or 2U holding 8 or 10 disks. If I understand SAS correctly, I'd probably have a unit with 2 SFF-8088 miniSAS connectors (although, I believe these connectors only support 4 devices, so if the JBOD is >8 disks, I don't know what would happen).

I'm completely undecided on the JBOD itself; recommendations here would be greatly appreciated. It's a bit of a shot in the dark.

I'd appreciate feedback and suggestions on the hardware above, or a discussion of the performance. (E.g. a discussion of SAS ports/bandwith, PCI express lanes/bandwidth, disks and network to determine the through put of this setup.)

Cheers,
Richard

I use a very similiar controllers, the LSI 3442X-R and 3442E-R. They have only one external connector, and this is a different connector type. It looks a bit more stable (mechanically), but this might be a matter of taste and I have never used the other connector type. (I had to update the controllers using the latest firmware available on the LSI web site.)

The JBODs that I am aware of use internal SAS port expanders (see
<http://en.wikipedia.org/wiki/Serial_Attached_SCSI#SAS_Expanders>). The connection to the host has four SAS lanes (the concept is similiar to the up to 16 lanes on a PCI-Express card). Each disk is connected via one SAS lane, and all these lanes are switched by the port expander. So you do not need 8 lanes on the host computer in order to connect 8 disks.

I use DELLs MD1000 JBOD (some with SATA, some with SAS), and it works fine. I have up to three JBODs connected to one SAS host port.

Currently I don't see limits that must be considered. Simple math with bandwidths. Nowadays I prefer PCI-Express over PCI-X. AFAIR the LSI cards have 8 PCI-Express lanes, so you need a matching port on the mainboard.

Sven