HP DL380p backplane - can I connect two HBA's at the same time?

[Kailee71]

Hi all,


I have a HP DL380p G8 LFF (12x 3.5" drives), and run esxi 7.0 on it, which boots from the integrated p420i from a mirror of 2 ssd's (not zfs, just a straight RAID volume). I pass through a Dell perc h310 to a TrueNAS 12.0-u1 vm which works really well. Currently I have both of the backplane connectors connected to the two ports on the h310, and so have to connect the two ssd's that hold the esxi boot volume with sas-to-sata cables to the sas connectors on the mainboard and mount the ssd's internally using a PCI disk mounting bracket. Of course for airflow inside the chassis this is not great so I want to ask if I can connect one of the Backplane connectors to the internal p420i and the other to the perc so that the two esxi ssd's can also be mounted in caddies and accessed from the front of the chassis... I tried this very briefly but was weirded out because suddenly all the TrueNAS disks showed up in the p420i's rbsu. I did not not up all the way to see if truenas saw its disks still as I got scared. Is this expected? Is this ok to do or am I lucky my zfs pool survived this experiment?

Many thanks in advance,

Kai.

 

[Kailee71]

Just to be clear - I'm not after hba redundancy or multipathing or anything, just wondering if I can boot esxi from the onboard raid controller and pass through the perc to the TrueNAS vm when both are connected to the same backplane...

 

[Kailee71]

Bump ... nobody has any thoughts on this?

 

[Samuel Tai]

I don't think this is a good idea. Backplanes expect to be connected to the same controller. Having one backplane connected to different controllers may work, if the backplane is wired as 2 independent backplanes, and it's not set up for multipath. However, this is a crapshoot, and you may end up with undefined behavior, like you experienced.

 

[jgreco]

SAS is designed to let you do stuff like this, but it may not be a great idea. It just takes one mistake for stuff to start overwriting things you didn't intend to.

 

[no_connection]

Have anyone actually tested if you could "jump ports" on a backplane and wreck a drive on a different cable?
I would assume backplane collects info and share it over both ports for redundancy, but it would be nice to know how it actually work and not guessing.
I intend to hook up one half to P420i and one half to onboard SATA but have not done any more experiments other than see it work.

 

[jgreco]

That's not how SAS works.

SAS has initiators and targets. An initiator initiates a request to a target, the target supplies the answer. The backplane acts in a role something like a dumb ethernet switch.

If you put two HBA's in your system, you have two initiators in a single system. SAS doesn't care. You can make a request to one target on the first and another target on the second. Or both initiators can be talking to a single target. There is no "backplane collects info and share it over both ports for redundancy." That needs to be done by the initiators on a host, which is what all the multipath logic is all about.

However, you cannot hook a SATA "initiator" to SAS. Doesn't work. SATA is tunneled over SAS using SATP.

 

[no_connection]

I did access the SATA drives through the SATA controller on the DL360e but I guess there could be more to it. It does say SATA controller in both OS and BIOS.
I have not looked closely but I really don't think these backplanes have data paths to access every drive from ether port. They are labeled 1-4 and 4-8.