PCIe slots are scarce but PCI slots are unused. Any recommendations for an eSata PCI board for the Drobo S to be used on Windows? I’m guessing the Drobo S is not faster than the bandwidth of PCI.
PCI Conventional (32-bit, 33 MHz) max bandwidth is 132 MB/sec. However, keep in mind that the PCI bus is shared with many other devices, depending on how the buses are connected on your particular motherboard (check the block diagram, if there is one). A good example is how on the Iwill DK8X motherboard, the Gigabit Ethernet controller is connected to the PCI bus, and therefore it does not achieve full 1 Gbps throughput.
Granted, the Drobo S transfer rates are around half the full PCI bandwidth, so YMMV.
How are your other drives connected, and what are your system specs? eSATA throughput can be limited by system speed and architecture.
I’m planning on building a new system from new parts and noticed that most motherboards are now in the smaller micro-ATX format, which means fewer slots. For example, a Gigabyte board for Intel has two PCIe x16 slots and two PCI slots. I would need one of the PCIe slots for video and the other for a tuner card, leaving me with just the two PCI slots. There is onboard SATA, but there is always a big chance none of the SATA ports support the required Port Multiplier feature. Complicating things is that some video cards these days are so big that they block adjacent slots or that some slots get disable when another particular slot is used. It’s a nightmare. The only reason I’m considering PCI is because I know the DROBO S’s main bottleneck is BeyondRAID and is far under the limit of any existing interfaces.
Perhaps DR should keep a database of supported cards and motherboards.
I’m not even sure why Port Multiplier is needed as I’ve seen other RAID boxes that don’t require this. Isn’t the storage on the DROBO virtualized and presented as one logical volume? Perhaps it’s for support of multiple volumes? What if I promise to never use more than 16TB of storage and only use it with a modern OS? 
As you guessed, Port Multiplier is to support Drobo’s Thin Provisioning. Port Multiplier support encompasses support for multiple LUNs (volumes), which is needed when you add more titles.
If you never go beyond one volume… I’m not sure.
Unless you’re capturing from a true, uncompressed HD source (like a game console, but not TV), PCI bandwidth is more than sufficient.
Digital TV signals are 25 Mbps (3.125 MB/sec) or less, so even if your card has four tuners, you’re still only at 100 Mbps (12.5 MB/sec), well within PCI’s theoretical max of 132 MB/sec. You could also use a USB tuner to save a slot.
While a PCI eSATA card won’t (shouldn’t) bottleneck transfer from the Drobo S, a PCIe eSATA card would give you much better throughput when using multiple drives as you won’t saturate the bus.
I’m just thinking out loud for future expansion, say, if you wanted to add more eSATA devices.
And if you are capturing some kind of raw uncompressed HD, then you will need PCIe bandwidth for that.
Also, a lot of esata cards only support 2TB volumes sizes, so if you have just 4 x 1TB drives, that’s 2.7 TB available for data, if you format for 2TB for the esata you got 2 volumes. So in order to see the 2nd volume on via esata you need the port multiplier.
So if my system can create and see the Drobo’s full 16TB primary volume, then I don’t need to worry about Port Multiplier support unless I somehow manage to put more than 16TB into the Drobo S? So Port Multiplier is optional if:
- Host OS can support more than 2TB (ie: Windows 7).
- Sata Controller can support more than 2TB volumes.
- There is no more than 16TB of drives (So on a system that doesn’t support Port Multiplier, then if there were more than 16TB of actual storage, would the worst result be just not being able to see the second volume?).
- Yes
- Yes
- Yes
So just to be perfectly clear… if those 3 requirements are met, then port multiplier support is not needed?
Yes.
Port multiplier is ONLY needed if you have more than 1 volume on your drobo. If you have 2 volumes and no port multiplier, you will only mount and see 1 volume on your computer.
Good to know. Thanks!
Hopefully the next WHS version supports GPT and I can have just one big volume per-Drobo.
I just realized that if the Drobo S is filled to capacity with today’s largest drives (2TB), the volume will only be 5 x 2TB = 10TB. And when 3TB drives come around, perhaps later this year, it’s still 5 x 3TB = 15TB, which is still under the 16TB volume limit. So port multiplier support is unimportant as long as you’re using an OS newer than Windows XP.
And that the eSATA card supports volumes larger than 2TB.