SubnetMask
Contributor
- Joined
- Jul 27, 2017
- Messages
- 129
I have a SuperMicro SAS2-826EL2 backplane coming for my FreeNAS 'Head', and have two LSI 9207-4i4e HBAs (I needed a SAS2 backplane for the JBOD enclosure I have as the SAS1 backplane it came with doesn't work with drives over 2TB, and the SAS2-EL2 wasn't much more than the SAS2-EL1 backplane). The primary 'goal' is HBA and backplane resiliency, so one of the expanders could fail, or one of the HBAs could fail, or a cable could fail, and the unit will (should) keep on going (let's be honest - the odds of any one of those failures is greater than '0', but the odds of more than one of those at the same time that takes the system down... I'll probably win the lottery first - it pretty much leaves motherboard failure as about the only thing that could take it down hard).
While odds of me saturating the 24Gbps 4-channel SAS link from the backplane on the first expander are pretty much zero (based on my rough calculations, you'd need about 15 drives running 200MB/s - and a way to get them ALL running 200MB's - to saturate four channels, so if you're running spinning disks, odds are that's NOT going to happen in a 12-bay enclosure - about the only way to have a chance would be an enclosure full of SSDs), but mostly for my curiosity, can that second expander on the second HBA increase and/or balance the bandwidth available out of the backplane? The SuperMicro documentation seems to indicate that you're actually not supposed to use 'Port 1' on the backplane for the HBA, but instead, it's supposed to be for cascading backplanes. The documentation does show dual HBA/dual expander configs (Port 0 on each expander going to a HBA), which is how I plan to cable it, but it's not abundantly clear on exactly how it works. Is it just for redundancy, or when everything's functioning normally, does it function as additional available bandwidth? Or can the backplane and expanders do anything and everything, and the limitation as to if it's redundancy only or redundancy and additional bandwidth comes down to the OS/Software? If the latter, how would FreeNAS handle it?
While odds of me saturating the 24Gbps 4-channel SAS link from the backplane on the first expander are pretty much zero (based on my rough calculations, you'd need about 15 drives running 200MB/s - and a way to get them ALL running 200MB's - to saturate four channels, so if you're running spinning disks, odds are that's NOT going to happen in a 12-bay enclosure - about the only way to have a chance would be an enclosure full of SSDs), but mostly for my curiosity, can that second expander on the second HBA increase and/or balance the bandwidth available out of the backplane? The SuperMicro documentation seems to indicate that you're actually not supposed to use 'Port 1' on the backplane for the HBA, but instead, it's supposed to be for cascading backplanes. The documentation does show dual HBA/dual expander configs (Port 0 on each expander going to a HBA), which is how I plan to cable it, but it's not abundantly clear on exactly how it works. Is it just for redundancy, or when everything's functioning normally, does it function as additional available bandwidth? Or can the backplane and expanders do anything and everything, and the limitation as to if it's redundancy only or redundancy and additional bandwidth comes down to the OS/Software? If the latter, how would FreeNAS handle it?
Last edited:
