I've decided to make the jump from HDDs to SSDs for my main storage and now i'm wondering if I needed to buy the backplane that bought. I have a supermicro CSE-846 24 bay case and it had the BPN-SAS2-846EL1 backplane. Right now I'm using 20 3tb spinning rust sas drives but I have bought 20 2tb ssds, THNSN81Q92CSE, to replace them. I know that the old sas2 backplane would have worked, but it was a single link expander so I know my bandwidth would have been limited by the backplane. So I bought the sas3 backplane, BPN-SAS3-846EL1, thinking it would allow for 2x the bandwidth but now that I'm thinking about it I'm not so sure. Will the fact that the drives are sata limit me to 4x the sata3 speeds or will the link be at the sas3 speeds? The HBA Ill be using is LSI YZCA-00424-101. Also Ill be using zfs with them and my plan right now is 2 vdevs, 10 drives wide raidz2 but just wanted to get anyone option on that as I'm no expert on zfs.
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Your drives should have max read speeds of 500MB/s so the max throughput for 20 is something like 10GB/s.
forums.unraid.net
This thread has examples for dual link sas2 vs your sas3 backplane. The short answer is something like 4 to 4.8 GB/s vs 6.6-7 GB/s.
Lsi has a feature called databolt which allows 12gb/s speeds when using sas2 or sata3 devices on sas3. The bandwidth on a pcie3 x8 is 8 GB/s so accounting for overhead you can saturate your HBA with the sas3 backplane and 20 drives assuming they are all being read at once.
So I think you could get another 1-1.5 GB/s or so with the sas3 backplane with a pcie4 hba. Probably not worth the investment though.
Also as far as I know just as an aside the supermicro sas2 backplanes actually support dual link even when documentation lists single link.
Sata/SAS controllers tested (real world max throughput during parity check)
I had the opportunity to test the “real word” bandwidth of some commonly used controllers in the community, so I’m posting my results in the hopes that it may help some users choose a controller and others understand what may be limiting their parity check/sync speed. Note that these tests are on...
forums.unraid.net
This thread has examples for dual link sas2 vs your sas3 backplane. The short answer is something like 4 to 4.8 GB/s vs 6.6-7 GB/s.
Lsi has a feature called databolt which allows 12gb/s speeds when using sas2 or sata3 devices on sas3. The bandwidth on a pcie3 x8 is 8 GB/s so accounting for overhead you can saturate your HBA with the sas3 backplane and 20 drives assuming they are all being read at once.
So I think you could get another 1-1.5 GB/s or so with the sas3 backplane with a pcie4 hba. Probably not worth the investment though.
Also as far as I know just as an aside the supermicro sas2 backplanes actually support dual link even when documentation lists single link.
Interesting, once I get everything in a may test out my new back plane in the same way he did. Would be awesome if it also has a dual link as I'm sure then the bottleneck would be in the cpu/ram of the system and not the link to the backplane. The system is just a 5900x with 3600mhz ram. I don't think pcie3 will be much of an issue as I know I'll never get 100% of the combined performance out of the drives. I'll be happy with 50% read and writes I know will be worse just from the nature of raidz. With that in mind even a 4xsas3 link may not be a bottleneck. I'm just happy to hear it is not going to be limited to 4xsata.
If anyone runs into this I can confirm that just like the BPN-SAS2-846EL1 the BPN-SAS3-846EL1 does have dual link. While scrubbing my pool I get 6.23 GiB/s with two cables going to my hba and if I unplug one of the cables it drops to 3.72 GiB/s. Looks like the limit now is the pci3 8x link.
I stumbled on your post as I was wondering about the BPN-SAS3-846EL1 myself. Which HBA card are you using specifically? I realize my LSI SAS9340-8i only has the 2x ports so I believe I'm limited to a single link (J49 vs J49+J50 connections) which is potentially impeding my current performance.
That said, perhaps I'm misunderstanding how you're achieving the dual links on the BPN-SAS3-846EL1. Any details would be fantastic, thank you!