[OmniOS-discuss] IDE mode and Advanced Format disks

[Hugh McIntyre]

I have a related question to the recent discussion of ashift=12 and 
advanced format disks.  The problem is that I have 4 disks attached via 
a LSI 9211-4i SATA/SAS adapter (which are fine) but several others 
attached via motherboard SATA connections and running in IDE 
compatibility mode.

The problem is that in IDE mode, the disks don't report any geometry 
information via format "inq", or "iostat -Er | grep -i vendor", and I 
only get the LSI-attached disks (plus a motherboard attached DVD drive) 
listed from "echo ::sd_state | mdb -k | egrep '(^un|_blocksize)'".

I'm sure all of these symptoms are linked, i.e. if the kernel does not 
know the disk geometry then iostat and format are not going to report it 
either.  But this seems like a problem for ashift detection logic that 
is not going to be able to get the geometry either.

(As an aside, no doubt I should have switched from IDE mode long ago ... 
but this is the default :( )

So my two questions:

1. If I change the SATA ports to AHCI instead of IDE in the BIOS, I'm 
guessing this will fix the bug, but I also assume this will change the 
paths under /devices and therefore make the system unbootable because 
one of these disks is a SSD containing the rootfs?  Is there a safe way 
to do this, or can I assume the paths will stay the same?  And would I 
get better performance in AHCI mode nowadays?  (This is a 
network-limited backup box so performance is not critical, but one 
partition of the SSD contains L2ARC used for dedup of some of the data).

2. Is this a bug I should file, with the possbility of being fixed, or 
just a limitation of the IDE layer that will never be able to get disk 
geometries and detect ashift cleanly?

Thanks,

Hugh.

PS: in my case, I worked around this by moving the disks around long 
enough to get the geometry, but a long-term answer would be good.


> https://www.illumos.org/issues/2665#note-3
>> http://wiki.illumos.org/display/illumos/ZFS+and+Advanced+Format+disks