Is there a more detailed explanation of why you need an HBA cross flashed to IT mode?

[oRAirwolf]

I have a friend that I recently convinced to switch from Solaris over to FreeNAS as his storage operating system. He built a backup server for his parents using an LFF Dell R320 with a Dell H310 mini SAS RAID controller. He has the drives set to passthrough in the controller, but it is not in P16 IT mode. He believes this is good enough and isn't interested in adding in a full size LSI HBA. I explained to him that FreeNAS needs to be able to read the smart data from the drives to monitor drive health and it cannot do this in its current configuration. My question is whether somebody can provide a more thorough explanation of the cons of not using an HBA in P16 passthrough mode so I can inform him and hopefully make sure his parents don't lose a bunch of irreplaceable data.

 

[Mirfster]

Excerpt from "FreeNAS: A Worst Practices Guide":

Finally, most hardware RAID cards will mask the S.M.A.R.T. disk health status information that each disk provides. Very simply, each disk is connected to the hardware RAID controller card and the disks become invisible to the standard S.M.A.R.T. monitoring utility “smartctl”. Without access to this information, the user is left unaware of classic warning signs of impending disk failure, like reallocated sector count or unusually high temperature. Even the time it takes to run smartctl can be indicative of an impending problem.

While some hardware RAID cards may have a “pass-through” or “JBOD” mode that simply presents each disk to ZFS, the combination of the potential masking of S.M.A.R.T. information, high controller cost, and anecdotal evidence that any RAID mode is about 5% slower than non-RAID “target” mode results in zero reasons for using a hardware RAID card with ZFS.

Long story short, using hardware RAID on FreeNAS can lead to anything from corrupted writes to fatal errors that require you to invest in costly data recovery services.

 

[oRAirwolf]

Excerpt from "FreeNAS: A Worst Practices Guide":

I appreciate the reply. I guess my question was if there is anything beyond that. Does it make migrating an array to a different RAID controller impossible? Are there performance issues? Reliability issues? Possible added risks for data corruption during writes? I'm just looking for anything beyond the concern with reading smart info.

 

[Chris Moore]

can provide a more thorough explanation of the cons of not using an HBA in P16 passthrough mode

The current firmware version that should be used is 20.00.07 in IT mode. The Mini SAS card can't do that though because it will brick the card.
If he don't want to change it, he could have a drive failing and not know about it. Enough drives fail and the pool is lost. If he ever used ZFS on Solaris, he should know this. It is the same way.

Does it make migrating an array to a different RAID controller impossible?

Yes, because the raid controller has created a virtual container inside the physical drive and that is what is being shared to the FreeNAS installation. It makes you need the same controller to be able to see the contents of the disks and that is a bad thing. It will keep you from moving the disks to another server, which you would normally be able to do.

Are there performance issues?

Yes, because the cashing controller between the OS and the drive can actually make the system slower and it can create data errors.

Reliability issues?

Yes, already mentioned them. It is just a bad idea all the way around.

Possible added risks for data corruption during writes?

Yes, that too.

You know the old saying, you can lead a horse to water but you can't make them drink? We have someone come in every two or three months insisting that they can use a hardware RAID controller, it always ends badly and they usually blame FreeNAS when it was a bad selection of hardware.