If one happens to have some server-grade hardware at ones disposal, is it ever advisable to run ZFS on top of a hardware-based RAID1 or some such? Should one turn off the hardware-based RAID, and run ZFS on a mirror or a raidz zpool instead?
With the hardware RAID functionality turned off, are hardware-RAID-based SATA2 and SAS controllers more or less likely to hide read and write errors than non-hardware-RAID controllers would?
In terms of non-customisable servers, if one has a situation where a hardware RAID controller is effectively cost-neutral (or even lowers the cost of the pre-built server offering, since its presence improves the likelihood of the hosting company providing complementary IPMI access), should it at all be avoided? But should it be sought after?
Best Answer
The idea with ZFS is to let it known as much as possible how the disks are behaving. Then, from worst to better:
As ZFS is quite paranoid about hardware, the less hiding there is, the more it can cope with any hardware issues. And as pointed out by Sammitch, RAID Controller configurations and ZFS may be very difficult to restore or reconfigure when it fails (i.e. hardware failure).
About the issue of standardized hardware with some hardware-RAID controller in it, just be careful that the hardware controller has a real pass-through or JBOD mode.