Just to chime in: it will look fine, feel fine, but underneath it's quite easy to get VMFS corruption. Happened in our tests.
Also if you're running LIO, from time to time expect a kernel panic (haven't tried with the latest upstream, as I've been using
Ubuntu 14.04 on my "export" hosts for the test, so might have improved...).
As of now I would not recommend this setup without being aware of the risks involved.
There have been a few upstream patches getting the LIO code in better cluster-aware shape, but no idea if they have been merged
yet. I know RedHat has a guy on this.
On 01/21/2015 02:40 PM, Nick Fisk wrote:
Hi Jake,
Thanks for this, I have been going through this and have a pretty good idea on what you are doing now, however I maybe missing something looking through your scripts, but I’m still not quite understanding how you are managing to make sure locking is happening with the ESXi ATS SCSI command.
From this slide
It seems to indicate that for a true active/active setup the two targets need to be aware of each other and exchange locking information for it to work reliably, I’ve also watched the video from the Ceph developer summit where this is discussed and it seems that Ceph+Kernel need changes to allow this locking to be pushed back to the RBD layer so it can be shared, from what I can see browsing through the Linux Git Repo, these patches haven’t made the mainline kernel yet.
Can you shed any light on this? As tempting as having active/active is, I’m wary about using the configuration until I understand how the locking is working and if fringe cases involving multiple ESXi hosts writing to the same LUN on different targets could spell disaster.
Many thanks,
Nick
From: Jake Young [mailto:jak3kaj@xxxxxxxxx]
Sent: 14 January 2015 16:54
To: Nick Fisk
Cc: Giuseppe Civitella; ceph-users
Subject: Re: Ceph, LIO, VMWARE anyone?
Yes, it's active/active and I found that VMWare can switch from path to path with no issues or service impact.
I posted some config files here: github.com/jak3kaj/misc
One set is from my LIO nodes, both the primary and secondary configs so you can see what I needed to make unique. The other set (targets.conf) are from my tgt nodes. They are both 4 LUN configs.
Like I said in my previous email, there is no performance difference between LIO and tgt. The only service I'm running on these nodes is a single iscsi target instance (either LIO or tgt).
Jake
On Wed, Jan 14, 2015 at 8:41 AM, Nick Fisk <nick@xxxxxxxxxx> wrote:
Hi Jake,
I can’t remember the exact details, but it was something to do with a potential problem when using the pacemaker resource agents. I think it was to do with a potential hanging issue when one LUN on a shared target failed and then it tried to kill all the other LUNS to fail the target over to another host. This then leaves the TCM part of LIO locking the RBD which also can’t fail over.
That said I did try multiple LUNS on one target as a test and didn’t experience any problems.
I’m interested in the way you have your setup configured though. Are you saying you effectively have an active/active configuration with a path going to either host, or are you failing the iSCSI IP between hosts? If it’s the former, have you had any problems with scsi locking/reservations…etc between the two targets?
I can see the advantage to that configuration as you reduce/eliminate a lot of the troubles I have had with resources failing over.
Nick
From: Jake Young [mailto:jak3kaj@xxxxxxxxx]
Sent: 14 January 2015 12:50
To: Nick Fisk
Cc: Giuseppe Civitella; ceph-users
Subject: Re: Ceph, LIO, VMWARE anyone?
Nick,
Where did you read that having more than 1 LUN per target causes stability problems?
I am running 4 LUNs per target.
For HA I'm running two linux iscsi target servers that map the same 4 rbd images. The two targets have the same serial numbers, T10 address, etc. I copy the primary's config to the backup and change IPs. This way VMWare thinks they are different target IPs on the same host. This has worked very well for me.
One suggestion I have is to try using rbd enabled tgt. The performance is equivalent to LIO, but I found it is much better at recovering from a cluster outage. I've had LIO lock up the kernel or simply not recognize that the rbd images are available; where tgt will eventually present the rbd images again.
I have been slowly adding servers and am expanding my test setup to a production setup (nice thing about ceph). I now have 6 OSD hosts with 7 disks on each. I'm using the LSI Nytro cache raid controller, so I don't have a separate journal and have 40Gb networking. I plan to add another 6 OSD hosts in another rack in the next 6 months (and then another 6 next year). I'm doing 3x replication, so I want to end up with 3 racks.
Jake
On Wednesday, January 14, 2015, Nick Fisk <nick@xxxxxxxxxx> wrote:Hi Giuseppe,
I am working on something very similar at the moment. I currently have it working on some test hardware but seems to be working reasonably well.
I say reasonably as I have had a few instability’s but these are on the HA side, the LIO and RBD side of things have been rock solid so far. The main problems I have had seem to be around recovering from failure with resources ending up in a unmanaged state. I’m not currently using fencing so this may be part of the cause.
As a brief description of my configuration.
4 Hosts each having 2 OSD’s also running the monitor role
3 additional host in a HA cluster which act as iSCSI proxy nodes.
I’m using the IP, RBD, iSCSITarget and iSCSILUN resource agents to provide HA iSCSI LUN which maps back to a RBD. All the agents for each RBD are in a group so they follow each other between hosts.
I’m using 1 LUN per target as I read somewhere there are stability problems using more than 1 LUN per target.
Performance seems ok, I can get about 1.2k random IO’s out the iSCSI LUN. These seems to be about right for the Ceph cluster size, so I don’t think the LIO part is causing any significant overhead.
We should be getting our production hardware shortly which wil have 40 OSD’s with journals and a SSD caching tier, so within the next month or so I will have a better idea of running it in a production environment and the performance of the system.
Hope that helps, if you have any questions, please let me know.
Nick
From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Giuseppe Civitella
Sent: 13 January 2015 11:23
To: ceph-users
Subject: Ceph, LIO, VMWARE anyone?
Hi all,
I'm working on a lab setup regarding Ceph serving rbd images as ISCSI datastores to VMWARE via a LIO box. Is there someone that already did something similar wanting to share some knowledge? Any production deployments? What about LIO's HA and luns' performances?
Thanks
Giuseppe
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