Supermicro 'TQ', 'A' Backplanes and SAS3

[K D]

Do they support SAS3 speeds if paired with a SAS3 HBA?

Is SAS3 speed difference worth the price difference if the primary use is going to be one large pool for media storage with one smaller SSD pool for VM Storage?

I got a really good deal on 2 NIB 846 Chassis with SAS1 backplanes that need to be replaced. I would prefer to get expander backplanes but the SAS3 expanders are too expensive.

One is going to be used as a JBOD to an existing server and I'll get a SAS2 expander backplane for it. The other one is for a new build. So I am wondering if it is worth getting a SAS3 expander or go with a direct attach.

Thoughts?

 

[ttabbal]

As I understand it, yes. I haven't tried it personally, but I have read reports that it works.

For SSD, if you are getting SAS3 SSDs, it might be worth it. For HDD pools, even SAS1 is fast enough for most setups. The biggest reason that you don't see more people using SAS1 is the 2TB limit. The only speed related reason for using SAS2 for most people on HDD setups is the channel between the HBA and expander.

 

[K D]

Thanks. Can you elaborate on this? Did you mean SAS3?

The only speed related reason for using SAS2 for most people on HDD setups is the channel between the HBA and expander.

 

[i386]

So I am wondering if it is worth getting a SAS3 expander or go with a direct attach.

That depends on your mainbaord and how many pcie slots you have: if just one is unused then get an expander backplane. If you have three available pcie slots get 3 hbas (or 1hba + expander on an add on card).

 

[i386]

So I am wondering if it is worth getting a SAS3 expander or go with a direct attach.

That depends on your mainbaord and how many pcie slots you have: if just one is unused then get an expander backplane. If you have three available pcie slots get 3 hbas (or 1hba + expander on an add on card).

 

[cheezehead]

The TQ-style and A-style backplanes for Supermicro are passive in nature. They cannot be dual-ported but will run at whatever the fastest speed matching speed is between the drive connected and the HBA being used.

If the worry is about a single SSD....you could always stick it somewhere else in the chassis and direct cable it off of the motherboard or another HBA port.

 

[ttabbal]

Thanks. Can you elaborate on this? Did you mean SAS3?

Nope. SAS2. HDDs just aren't fast enough to be concerned about it if you're direct cabling. Particularly in a server where most work will be random in nature.

I started with SAS1 cards, 2 6-disk raidz2 array. When building my new server I upgraded to SAS2 mostly due to the 2TB limit. As an experiment, I swapped the cards in the existing server. No change in performance. You might benchmark a very slight difference on very heavy sequential workloads, but in real life sequential performance just doesn't happen on servers. It's pretty rare on desktops these days with multitasking, which is why even low end SSDs help so much on desktops.

Now, if you're putting disks behind an expander, that goes out the window. You generally have a 4-port connection to the expander from the HBA. If you load up a 24 drive chassis, I could see throughput being limited over that connection due to SAS1. Maybe even SAS2, but I haven't tried it.

There are exceptions to everything, so if your HDDs happen to be some crazy fast model, it might matter. But even if you think that's you, you might want to test it. Why spend the money on SAS3 if you don't need it? It's a bit like connecting a 1gbit ethernet card to a 100Mbps switch. You can, but it's not going any faster. Where SAS2 cards go on ebay for about $40, it's a cheap test and if you decide it's not fast enough, you can use it for something else or sell it here. There's always people looking for SAS2 HBAs around here.

SSDs, good ones anyway, can likely sustain random speeds high enough to matter. Which is one reason PCIe SSDs are a thing now.

 

[K D]

@ttabbal . Thanks for the detailed response. I'm going to be using a pool of spinners for media storage and a pool of SATA ssds for VM storage. The media storage will definitely not benefit from sas3 speeds. The VM Storage was what I was concerned about. I plan to have 3 diskless esxi hosts boot off iscsi from this server and also have the server provide nfs storage for the esxi hosts.

I do have both sas3 and sas2 hbas. Ive gone ahead and ordered one TQ backplane and one SAS2 backplane. Will tweak and rebuild if needed.