iSCSI initiator and Dell PowerVault MD3000i
danny at cs.huji.ac.il
Mon Dec 21 11:20:55 UTC 2009
> Daniel Braniss wrote:
> >> So instead of iSCSI connected storage with multipath failover, I got
> >> singlepath storage causing system freeze in case of network disconnection :(
> > well, if you unplug the net, or reboot the target, it will recover.
> > it's when you down/up the network when problems occur, and I'm
> > looking into it.
I took a machine, with 2 nics, connected to 2 vlans,
A is the default, B is on the same vlan as my target iscsi server.
if I unplug or do an 'ifconfig netB down', the iscsi_initiator
will recover - after about 1 minute - reconnecting to the target via netA
> Just the note to my tests with multipathing. I asked about MD3000i one
> friend who is aware of DELL arrays and he told me that it is
> 'active/passive' / 'dual active' type of array and Virtual Disks (LUNs)
> are always accessible only by one controller. In case of failure of
> currently active controller path, the driver must send some command to
> the other controller to take ownership of the LUN to this controller.
> I searched the net for some more information and it seems that it is
> handled by RDAC on Linux
> (http://fxr.watson.org/fxr/source/drivers/md/dm-mpath-rdac.c?v=linux-2.6) but
> we don't have it in FreeBSD?
> Do you have some knowledge about this? Is it something that can be done
> in iSCSI or is it something for another part / layer in the FreeBSD?
Let me see if I can untangle all these acronyms :-)
iSCSI is scsi over ip, it's 'usually' presented some 'scsi device',
tape, disk, via some target. It's the target that controls the real
hardware, so a hardware error at the raid controller level cannot be
handled by the initiator (so no RDAC), specially when the target provides
a virtual disk (which is about 100% true for all the targets I have
encountered so far).
A RAID controller is not a SCSI device, and so it can't be controlled
by the iSCSI initiator.
Multipath, in iSCSI it means more than one network path to the same
target/lun, the current iscsi_initiator does not handle this, but since istg
handles this, I'm looking into it.
it would be helpful if you can describe what you are trying to accomplish.
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