On 06/23/2010 09:34 AM, Christopher Barry wrote:
correction inline:
On Wed, 2010-06-23 at 10:28 -0400, Christopher Barry wrote:
Hello,
I'm implementing some code to automagically configure iscsi connections
to a proprietary array. This array has it's own specific MPIO drivers,
and does not support DM-Multipath. I'm trying to get a handle on the
differences in redundancy provided by the various layers involved in the
connection from host to array, in a generic sense.
The array has two iSCSI ports per controller, and two controllers. The
targets can be seen through any of the ports. For simplicity, all ports
are on the same subnet.
I'll describe a series of scenarios, and maybe someone can speak their
level of usefulness, redundancy, gotchas, nuances, etc:
scenario #1
Single NIC, default iface, login to all controller portals.
Of course with this there is no redundancy on the initiator side. If the
nic on the initiator side dies, you are in trouble. And if you are not
using multipath software in the block/scsi or net layer then logging
into all the portals is no use.
Using dm-multipath across the target ports for most targets works well,
and would allow you to take advantage of redundancy there. Can't say
anyhting about your mpio code you are using or your target since I do
not know what they are.
scenario #2
Dual NIC, iface per NIC, login to all controller portals from each iface
Without some multipath software then this is pretty useless too. If you
use something like dm-multipath then it can round robin or failover over
all the paths that will get created.
scenario #3
Two bonded NICs in mode balance-alb
Single NIC, default iface, login to all controller portals.
single bonded interface, not single NIC.
I do not have a lot of experience with this.
scenario #4
Dual NIC, iface per NIC, MPIO driver, login to all controller portals
from each iface
The iscsi/scsi/block layers provide what dm-multipath needs for this,
and for most targets it should work. Again, I have no idea what your
MPIO driver does and needs so I cannot say if it will work well for you.
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