PCI-e SATA expanders???

[tmacka88]

Hi,

I looking at expanding my NAS and I'm after a way to use more SATA HDD's I have a PCI-e x4 and a PCI-e X16. Now I have seen some PCI-e SATA cards but not sure if they are compatible with freenas. If anyone knows which ones are and if they are any good. Im currently looking at a

Syba SY-PEX40008
http://www.sybausa.com/productInfo.p...&currentPage=0

Im not sure if the performance is going to drop on this as it supports 4X SATA 2 @ 3Gbps, although it is only a PCI-e running at X1. I believe that X1 is 2.5Gbps (correct me if I'm wrong) so if so will this bottle neck my RAIDz setup?

Thanks

[Milhouse]

That's not a SATA Expander - a SATA (SAS) Expander is a card that connects to an existing HBA (ie. SAS/SATA Controller) and expands the number of SAS/SATA devices that can be connected/addressed, eg. this Chenbro Expander which only uses the PCIe slot for physical support, not power or data signals.

A PCIe x1 slot is only capable of 250MBytes/sec (v1) or 500MBytes/sec (v2), so not really sufficient for the theoretical 4x SATA2 disks @ 3Gbps each, although in reality you'll be doing well to get a SATA2 HDD to sustain 50MBytes/sec in which case an x1 v1 slot may be just fine.

As for that particular card, the controller chipset is the most important aspect of it in which case I would suggest checking for any known compatibility issues with the Sil3124 and FreeBSD (a quick Google suggests it is supported quite adequately in FreeBSD 8 and so should be supported by FreeNAS 8).

[tmacka88]

How about port multipliers, such as

http://www.ebay.com.au/itm/SATA-II-I...ht_4280wt_1185

these seem to be cheaper than the SAS

[Milhouse]

Yep, that should work too.

I'm certainly not an expert on Expanders or Port Multipliers, but I'm assuming they work by "sharing" the bandwidth of the uplinked HBA connection across all of the expanded/multiplied ports, which may mean a significant reduction in average disk I/O? For instance, if one SATA2 port is multiplied to become 5 SATA ports (as seems possible with the card from post #3) then the *theoretical* 3Gbits/sec of SATA2 bandwidth is now being shared across 5 ports, meaning each of the 5 ports - in a worst case situation - may average no more than 600Mbits/sec. However in terms of real world performance, I have no idea how this will work out - perhaps disk bandwidth will still be sufficient for "good" performance with SATA2 HDDs, considering they rarely hit 500Mbit/sec anyway?

[jgreco]

I'm reminded of an argument I had a long time ago with some internet engineer who was getting all freaked out about the need for fast/wide SCSI on his server; I brought the discussion to an end by pointing out that fast SCSI was basically 80 megabits per second, his server only had a 100Mbps interface (which was tops back then), and that his entire ISP only had a 45Mbit/sec connection to the Internet.

Your theoretical 3Gbps of SATA2 bandwidth may not be a significant impediment if you only have 1x or 2x 1Gbit ethernets on the server. Just another way to think about the problem.

[cypher1024]

I know for a fact that these Dell SAS 5 cards work with FreeNAS: http://www.ebay.com.au/itm/Dell-P-N-...item335e64acfd
You'll also need a SFF-8484 to 4xSAS/SATA 7-pin fanout cable like this: http://www.ebay.com/itm/New-32-Pin-S...item1e647c4aca
Then you need to figure out a bracket to mount it. Here's my solution: http://forums.freenas.org/showthread...et-Fabrication

[tmacka88]

what kind of speeds do you get out of the dell SAS card? would it support 100MB/s for all 4? or more?

[mav@]

Syba SY-PEX40008
http://www.sybausa.com/productInfo.p...&currentPage=0

Im not sure if the performance is going to drop on this as it supports 4X SATA 2 @ 3Gbps, although it is only a PCI-e running at X1. I believe that X1 is 2.5Gbps (correct me if I'm wrong) so if so will this bottle neck my RAIDz setup?

This card is well supported by FreeBSD and should work well in FreeNAS 8. Respecting its PCIe 1.0 x1 interface it is effectively able to pass up to 200MB/s total. Actually that is maximum I've seen from cards on that bus. Also (if needed) it also has one of the most effective support for SATA port multipliers -- it is able to completely saturate SATA link with five devices on multiplier working simultaneously. So if 200MB/s is enough for you, its not a bad choice. Looking that card is not expensive and often there are several PCIe slots available, you may put as many cards as you need to reach target capacity and performance.