Hacker News new | ask | show | jobs
by topspin 675 days ago
> and doesn't work with filesystems that do their own redundancy like ZFS

Really? You somehow can't create a ZFS file system on an hardware RAID block device? Seems like that means the hardware RAID isn't the otherwise transparent block device it's supposed to be for the OS and whatever file systems it cares to employ.

You're concerns about management, tools and spares are correct for many use cases. Some uses cases, like cloud operators that don't suffer the burdens of long term management at that level of detail (where entire racks and generations of hardware are cycled in/out as a working unit, with ample spares at hand, under contract) won't care about that. They'll care about the nice efficiency gain. When you operate like that you can accommodate sophisticated integration such as this for efficiency gains.
1 comments
sliken 675 days ago
> Really? You somehow can't create a ZFS file system on an hardware RAID block device?

Sure you can do it, have two layers of checksums and a volume manager on top of a volume manager. But ZFS is designed to talk directly to block devices and try to detect and complain about the numerous failure modes. Like say a parity calc that goes awry because of a memory error.

For this and other reasons it's recommended that even with Hardware RAID it's recommended to configure it in JBOD mode.

I've also seen numerous cases where software RAID on top of hardware RAID running in JBOD mode is faster than just using hardware RAID.

> When you operate like that you can accommodate sophisticated integration such as this for efficiency gains.

Sure, if there are efficiency gains. If the strong bottleneck for writing to the controller is your limiting factor you might get a 33% increase in I/O. But for that to be true you need:

  * The bottleneck not to be elsewhere
  * The controller inside a NVMe device (often passively cooled) to be faster than the one on the CPU
  * The bandwidth between the PCI controller or PCIe switch and the NVMe controller to not care about a 2x increase in needed bandwidth
Seems unlikely to me.
link