From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Clements Subject: Re: Problems with software RAID + iSCSI or GNBD Date: Tue, 28 Jun 2005 21:11:39 -0400 Message-ID: <42C1F54B.1060405@steeleye.com> References: <42BF67A2.6040601@nighthawkrad.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <42BF67A2.6040601@nighthawkrad.net> Sender: linux-raid-owner@vger.kernel.org To: Christopher Smith Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Christopher Smith wrote: > stitch it together into a RAID1. So, it looks like this: > > "Concentrator" > /dev/md0 > / \ > GigE GigE > / \ > "Disk node 1" "Disk node 2" > > So far I've tried using iSCSI and GNBD as the "back end" to make the > disk space in the nodes visible to the concentrator. I've had two > problems, one unique to using iSCSI and the other common to both. Personally, I wouldn't mess with iSCSI or GNBD. You don't need GNBD in this scenario anyway; simple nbd (which is in the mainline kernel...get the userland tools at sourceforge.net/projects/nbd) will do just fine, and I'd be willing to bet that it is more stable and faster... > Problem 2: The system doesn't deal with failure very well. > > Once I got the RAID1 up and running, I tried to simulate a node failure > by pulling the network cable from the node while disk activity was > taking place. I was hoping the concentrator would detect the "disk" had > failed and simply drop it from the array (so it could later be simply > re-added). Unfortunately that doesn't appear to happen. What does > happen is that all IO to the md device "hangs" (eg: disktest throughput > drops to 0M/sec), I am unable to either 'cat /prod/mdstat' to see the md > device's status or use mdadm to manually fail the device - both simply > result in the command "hanging". Well, that's the fault of either iSCSI or GNBD. md/raid1 over nbd works flawlessly in this scenario on 2.6 kernels (for 2.4, you'll need a special patch -- ask me for it, if you want). -- Paul