I have a M1015 in passthrough (esxi 5.1). Now I want to create a zfs2 system with 10 disks (8+2 parity).
Can I use rdm ( http://blog.davidwarburton.net/2010/10/25/rdm-mapping-of-local-sata-storage-for-esxi/ ) for the remaining two drives? (These two drives are attached to the standard AHCI ports of the intel z77 / i7-3770 motherboard. Unfortunately passingthrough this AHCI panther controller will break the esxi system - even with the datastor (which contains openindiana) on a simple, separate pxie1 controller - bummer).
Will rdm disks combined with M1015 passthrouged disks impair the safety of the zfs z2 data in any way?
I haven't done any testing with RDM myself but in theory it won't be less safe probably but it is a lot harder to maintain. If a disk fails and needs replacing or moving it will be a bit of manual fiddling and maybe some downtime.
If you want to test to see if it will be safe and not cause problems I would recommend creating a pool (with no important data on it!) and then while the SAN VM is offline switch a drive from the M1015 to the onboard and one the other way around. Re set up the RDM mapping for the drive you moved to onboard and boot the SAN VM back up. If your pool detects the drives fine and works then you should be all good and safe. Also gives you an idea of the steps you may need to do later when fixing failed disks or reconfiguring your setup.
Also note that you can try upgrading to the latest patched version of ESXi 5.1 as I found this fixed a problem I was having getting the motherboard onboard controller to pass though in 5.1. This may let you do it properly without using RDM. If you are using standalone ESXi to do the upgrade you need to download a zip file with the latest patches and copy it to a local datastore then SSH in and run a special command to install the zip (esxcli software vib install -d *full path to uploaded zip*).
Edit: but this does not seem to be your problem as an earlier post you said you were already on the latest patch sorry. The best plan would be to get a second M1015 if possible ( this covers you for if one of them fails as well as you can move the extra 2 drives to RDM in an emergency if this happens. Another option is to get a better HBA to boot ESXi and store the local datastore. It is normally possible to get it to work but it can depend on the motherboard and the boot config options in bios.