Mapping VDIs directly to software iSCSI LUNs in XenServer

iscsilunnexentavdixenserver

I read in the XenServer Administrator's Guide in section 4.1.6.2 that you can map raw LUNs to VDIs if you're using a NetApp or EqualLogic SAN. Is it possible to do the same with Software iSCSI SANs (i.e. using a Nexenta/ZFS-based SAN as the iSCSI target)? I know I could setup an iSCSI SR and put VDIs on there, but I'd like to avoid it since I'd otherwise have to deal with the overhead of LVM, plus it'd make cloning more difficult. I'd handle the snapshotting and cloning from the SAN. So I'm basically just wanting to use a one-LUN-per-VDI mapping, without involving LVM inside the XenServer host.

I'm not opposed to setting this up through the CLI if necessary. I'd prefer something reliable that will persist across reboots of the XenServer host, but if I have to script something that will initialize the iSCSI sessions before the VMs start and the VDIs are loaded, I'm OK with that.

Best Answer

Figured it out. There is an undocumented "iscsi" SR driver that will create a LUN-per-VDI SR (I found this when looking through the /opt/xensource/sm directory - see the ISCSISR.py file). You can only set this up through the command-line, including creating the VBDs and attaching it to VMs. The VBDs and VDIs don't even show up in XenCenter.

Here's a sample command to set it up:

xe sr-create name-label=san type=iscsi device-config:target=<IP address of target> device-config:targetIQN=<IQN of target> shared=true

This will automatically create an VDI for each iSCSI LUN. If you end up adding a new iSCSI LUN on the SAN, XenServer will add a new VDI for it after executing the following command:

xe sr-scan uuid=<UUID of SR>

Also, if you end up resizing a LUN, XenServer does not automatically pick up on that, so you'd have to execute the following:

xe vdi-forget uuid=<UUID of VDI that you resized>
iscsiadm -m node -R
xe sr-scan uuid=<UUID of SR>

And to create a VBD and attach it to a VM:

xe vbd-create vm-uuid=<UUID of VM> device=<VBD device #, e.g. 0> vdi-uuid=<VDI of UUID>

Related Solutions

P2v options within a hyper-v environment

I use Citrix XenConvert to P2V our Windows servers into Microsoft Hyper-V. Yes, it was designed to be used with Xen, but it offers VHD as an output file type, and it is very effective. In all instances to date, the hosts have been running Hyper-V on Server 2008 x64 Standard or Server 2008 R2 Standard, and the guests have been running Server 2003.

I don't see any reason why this procedure wouldn't work on a server that boots from SAN:

First, I run XenConvert on the physical server while it's running (but outside of production hours). Then, I create the new virtual server with a Legacy Network Adapter, map the drive(s) to the VHD file(s) that I've created with XenConvert, shut down the old server, and fire up the new virtual server. It is easiest to RDP into the newly virtualized server to install Integration Services, because the mouse will not work via the Hyper-V console until they are installed. It's also possible to do via the keyboard on the Hyper-V host, but only in full screen mode: otherwise key combinations like ^-Esc go to the host.

I too have tried Disk2VHD and found it to be flaky. XenConvert works better.

[edit] download link: http://www.citrix.com/English/ss/downloads/details.asp?downloadId=1862307&productId=683148#top

Cheers,

Miles

Handling XenServer snapshotting and cloning with ZFS SAN

As other answers alluded to, the ideal approach is LUN-per-VDI. At first it didn't look like it was possible to do this, but there is an undocumented "iscsi" SR driver that will create a LUN-per-VDI SR (I found this when looking through the /opt/xensource/sm directory - see the ISCSISR.py file). You essentially setup one SR for each iSCSI target, and XenServer creates the VDIs for each LUN on that target. You can only set this up through the command-line, including creating the VBDs and attaching it to VMs. The VBDs and VDIs don't even show up in XenCenter.