Zfs and raid controllers

[Livesundersink]

I am currently setting up a file server and i was wondering how zfs works with raid controllers as i may be using one with a pair of ssd's to use as a cache, but i am in need of advice as to whether this is something I should or should not do

[Electronics Wizardy]

It will work fine, but its recommended to use a hba instead.

 

Often using a l2arc won't really help much in zfs anways, whats your usecase and hardware?

[dalekphalm]

On 6/29/2019 at 11:51 PM, Livesundersink said:

I am currently setting up a file server and i was wondering how zfs works with raid controllers as i may be using one with a pair of ssd's to use as a cache, but i am in need of advice as to whether this is something I should or should not do

You need to either use a true HBA (or other direct drive connection like a SATA port on the motherboard), or you need to ensure the RAID Controller is in IT mode (initiator target - which is “HBA” mode, basically). 

 

You technically can use a RAID Controller in IR mode (standard RAID firmware), but FreeNAS will not be able to tell proper drive health or stats, so you’re at larger risk for unexpected failures. 

[Windows7ge]

You do not want to use a RAID controller with ZFS, ZFS likes direct access to the drives. Use either an HBA or a RAID card that has been flashed to IT mode.

 

For the application of a File Server don't waste your time with an SSD cache. For read operations ZFS uses system RAM for frequently accessed files. For writes a cache will only work to accelerate synchronous operations. File Server operations are primarily asynchronous. The SSD will only take in data as fast as the pool can accept it making using it worthless.

[alex75871]

Don't. Use. RAID. Controller.

 

HBA or MB SATA in pass-through mode only.

[dalekphalm]

21 hours ago, alex75871 said:

Don't. Use. RAID. Controller.

 

HBA or MB SATA in pass-through mode only.

RAID controllers can be used, as long as they are running the IT Mode Firmware. In such a case, they're effectively an HBA.

 

Aside from that, if the Firmware is IR Mode, it will still work, but none of the SMART data will be properly readable by FreeNAS, so it's risky.