I'm looking for an HBA with write caching, and data loss protection for the cache, that's suitable for FreeNAS. The disks will mainly be writing/sync, so fast write response is useful.
Its easy to find RAID cards with write caching but ZFS really needs sight of the original disk, so a lot of pages recommend an HBA, or at worst, a RAID card with its onboard RAID disabled or not in use. LSI MegaRAID cards are said to be doubtful even used this way, because they obscure too much low level info about the disk from ZFS; I don't know if this issue affects all RAID cards or just LSI-based ones.
I don't mind if ZFS has very slight limitations (for example if it can't read SMART or needs a reboot to swap a failed drive) as long as basically it will work properly for data, and the card provides ZFS with fast write-back cache acceleration of drive writes that's protected against power loss. Some pages suggest that if that's acceptable, MegaRAID might be viable after all. But I don't know what else might be affected.
So what I think I'm after is either (1) an HBA rather than a RAID card, or at worst (2) a RAID card with true HBA mode as well as RAID, or (3) any controller card that can handle JBOD well enough that ZFS will be happy anyway.
My criteria are:
- Compatible with FreeBSD/FreeNAS.
- Gives a "good enough" view to the OS of the actual disks that ZFS will be happy and not have data safety issues with it.
- PCIe v2/v3 x4/x8 with "normal" PCIe connector.
- Either 2GB or 4GB of cache, ideally flash backed DDR for durability (of nvram, data retention after power failure, and no battery replacement every 3 years) but battery would be Ok if not.
- Not locked to a specific motherboard or family (I don't know if cards are sometimes locked to their manufacturer's motherboards but if so its not workable for me).
- Reliable brand/chips/firmware/drivers
- Fast, accepting and acknowledging writes to cache at least around 90k IOPS and 800 MB/s, and ideally if possible closer to 200k and 1.5-2.5 GB/s (multiple 10G NICs).
- Doesn't have to be a current product as I plan to buy 2nd hand on EBay if possible, but probably won't be too many years old because of other requirements. My guess is "good for the time" 2007 or later. Not sure if age means the supercap/battery is dubious and buy an older card + new supercap/battery.
- Not too fussy whether SAS or SATA, ideally SAS 12gb/s and 8 internal ports but this is flexible.
- Widely used or sold may help to keep price down and availability up.
- Rather obviously, write caching not disabled in HBA mode if relevant, and will play nicely with ZFS (doesn't 'hide' the disk itself or at least doesn't hide it too much)
I've tried to look online. Suggestions I've seen mentioned are:
- MegaRAID with multiple single disks, and accept the limitations on SMART/hot swapping (and hope it works otherwise?)
- Maybe some of the HP Smart Array controllers (but which?). This might be the most promising, I can see many on EBay and separately, fbwc modules for sale as well. But are they just rebadged LSI controllers and will any of them be OK for the platform and ZFS, and meet my needs?
- Maybe a native HBA or a RAID controller with a good HBA mode that has flash backed ram write cache (fbwc) but can't find details of any such models.
Can anyone recommend a suitable card - or at least card family - that would do this? Multiple possibilities would help in case availability varies.