SATA Port Multiplier vs PCI SATA Controller

[DoeBoye]

Hello all,

 

Just looking for some opinions. I find myself in the unfortunate situation where my chassis has 4 more bays available, but I have no more sata/sas ports available . My options now appear to be to use the one remaining pci (NOT -e) slot or use a port multiplier from a SATA III port on the mobo. The numbers seem to indicate that a port multiplier will give me much better performance. This is my thinking:

 

SATA III : 600 MB/s / 5 (4 new drives + 1 drive that was removed from the SATA3) = 120 MB/s per drive

PCI : 133 MB/s / 4 = 33.25 MB/s per drive

 

Now, my only concern, having no experience with port multipliers, is perhaps there is some extra overhead involved with using a port multiplier that does not show up in the numbers above...

 

Thoughts?

 

 

[BobPhoenix]

Never had good luck on Windows with port multipliers it is probably different with linux/unRAID.  My problem was Windows would drop the drives connected to the port multiplier every month or so.  If this is to your EP2C602-4L/D16 MB and M1015 controller then I would suggest using a SAS expander to expand your port count.  It would be much better than the port multiplier.  That of course assumes the box is the one listed in your sig.

Edited March 3, 2017 by BobPhoenix

[DoeBoye]

It is for the EP2C602, but the problem is that there are no more pcie slots available. The sata port multiplier I was looking at does not need to be plugged in to the mobo to work. I could put it in the position of the pci slot, plug in a molex, and I'm good to go... Or at least that's the theory :-)...

[BobPhoenix]

3 minutes ago, DoeBoye said:

It is for the EP2C602, but the problem is that there are no more pcie slots available. The sata port multiplier I was looking at does not need to be plugged in to the mobo to work. I could put it in the position of the pci slot, plug in a molex, and I'm good to go... Or at least that's the theory :-)...

I understand you have no more PCIe slots available that is why I suggested a SAS Expander to use with your IBM M1015.  If you use the same model I have (Intel RES2SV240) it has a molex for power.  It does NOT need to be plugged into a slot but it CAN be if you don't want to use the molex for power.  Just put electrical tape over the circut traces so you don't short anything out.  You would use a SFF-8087 to SFF-8087 cable to go from your M1015 to the RES2SV240.  From that you would use more SFF-8087 to SFF-8087 cables to go to the back planes on your Norco 4224.  That is how I have two of my servers setup. One M1015 to one RES2SV240 for 24 SATA port connections for each server.

[DoeBoye]

I didn't realize it didn't need to be plugged in! It lists pci-e x4 in the specs, but as you say, it doesn't need it... The only problem is it sells for $370 on newegg.ca... Maybe I can source a used one off Ebay. Thanks for the tip!

[DoeBoye]

Now that said, if I can't source a cheap one on ebay, has anyone had experience with a plain old sata multiplier? Are they as problematic in unRaid as they are in Windows for BobPhoenix

[ken-ji]

Hmm. Most MB's don't have port multiplier support on the SATA ports. Most of the time you'll need a SATA card, but Port multipliers only seem to work with SIL3132 chips

It should be fine, but in my experience they sometimes drop out the entire set of discs at once. I guess it depends on the quality of card and enclosure you are using.

 

[BobPhoenix]

Another option would be to replace the M1015 with an LSI 9201-16i.  It has 16 ports available instead of 8 so you would have the 4 more you need plus 4 extra.  But that is also expensive.  I bought mine for about $384 (If I remember correctly) off of Amazon.  Your Marvel 9230 based controller is a candidate for using a port multiplier but with my EP2C602-4L/D16 I found wouldn't work reliably for me with unRAID - why I bought the 9201 and replaced a M1015.  You might have better luck then I did with the Marvel controller.  I was passing it (9230 Marvel) through to a WHSv1 VM and every 3+ weeks it would drop the drives (same problem I had with my port multipliers on an earlier server).  I needed VT-d so I couldn't turn that off and I have the latest bios installed already and adding iommu=pt had no effect which are three of the recommendations in this thread for it:

 

Edited March 3, 2017 by BobPhoenix

[RobJ]

On 3/2/2017 at 5:20 PM, DoeBoye said:

Just looking for some opinions. I find myself in the unfortunate situation where my chassis has 4 more bays available, but I have no more sata/sas ports available . My options now appear to be to use the one remaining pci (NOT -e) slot or use a port multiplier from a SATA III port on the mobo. The numbers seem to indicate that a port multiplier will give me much better performance. This is my thinking:

 

SATA III : 600 MB/s / 5 (4 new drives + 1 drive that was removed from the SATA3) = 120 MB/s per drive

PCI : 133 MB/s / 4 = 33.25 MB/s per drive

 

Now, my only concern, having no experience with port multipliers, is perhaps there is some extra overhead involved with using a port multiplier that does not show up in the numbers above...

 

This is just my opinion, and based on poor memory too...

 

I don't like either of those options (not what you want to hear!).  I think both of those numbers are too optimistic.  As I recall (and I could be wrong), PCI transfers were not bidirectional like the SATA speeds, so you would have to split them in half or a lower.  I suspect a true max for 4 simultaneous transfers on PCI would be closer to 15MB/s.  But of course, you are rarely ever doing simultaneous I/O, except during parity operations or drive rebuilds.  When it's I/O to only one drive, which is most of the time, then you are back to full speed.

 

And Port Multipliers have always been very disappointing I think.  I don't recall ever hearing someone very satisfied with them, both for performance reasons and for reliability reasons.  Many Port Multipliers claim to support 5 drives, but the first or fifth drive would either be inaccessible, or would drop out periodically.  Again, it's been quite awhile, my memory could be very imperfect...  I'm also not sure you can find a SATA III port multiplier.  Most are older, require something like the SiI3132, which has its own top limits, is SATA II.

 

I think BobPhoenix's ideas are much better.

[DoeBoye]

Thanks for all the feedback, guys! Food for thought! I'm definitely going to need to do some more research