Xen Server Management

[tmcd35]

Although I am a self-confessed VMWare nut, even I can't totally justify their pricing and insistence on buying support wether you need it or not. So with that in mind I'm taking my first proper looks at Xen (it's free!).

My Linux knowledge is not to hot, so I was wondering if someone could explain some of the following to me.

If I set up three servers, how do I get them to access the same LUN. AFAIK if one OS has the LUN is would be locked to the other OS's. VMWare got around this by using their own FS, VMFS, that locks at the file level instead. I would want to store all my VM's on said LUN then run them accross 2/3 Xen servers.

Also, I understand that Xen can do Live Migration. I assume this needs all servers accessing the same LUN to work. Does Xen do automatitac Load Balancing with Live Migration? Also can it do the equivalent of VMWares High Availability - so if server fails it auto restarts on one of the other servers?

Finally, what software so you use to manage the servers/vm's? Is there a Xen equivalent of Virtual Center and Virtual Infrastructure Client in VMWare. It would be good to manage 2/3 servers from 1 (pref. Windows based) app.

[powdarrmonkey]

LUN?

Xen is free if you only want the stripped-down. It won't do live migration unless you pay IIRC (I may be wrong).

[tmcd35]

LUN?

Logic Unit Number (I think) - Basically a hard drive partition on a SAN. I want to assign a partition/LUN to store VM's and then run those VM's on any Virtual Server.

I can do this under VMWare - but at a prohibitive cost.

[CyberNerd]

AFAIK you need to set up some sort of filesystem clustering so that one OS will lock the LUN. I started looking into this, and I'm pretty sure it can be done with CLVM (a clustered LVM) rather than the overhead of GFS.
Configuring and Managing a Red Hat Cluster
There is comprehensive documentation here:redhat.com |


Xen can certainly be setup for high availability auto migration (heartbeat?), but I'm not sure about load balanced - no doubt there is a hack for it though.
Citrix Xen can do it, so I suspect the OSS xen can too.

Remember though, XEN is Citrix territory now. RHEL bought Qumranet (KVM) so future RHEL products will be KVM based, they'll keep supporting xen for the next 7yrs or so - so any GUI will want to support both (libvert based)

The other thing to look for is Sun's XVM
Sun xVM

I'm still slightly more in the ESXi camp - the migration tools are too good, I can probably live without live migration for now.

[Ric_]

Sun's xVM will be the way forward but they have not committed to a release date yet.

With Citrix XenServer Enterprise you get your XenMotion and a Windows Management console which are two things you seem to be after. For shared access to LUNs you allocate the LUNs to multiple servers and set the storage repositories up as lvmohba (LVM over HBA)... it's quite easy if you follow the instructions. There's also P2V utilities if you like that sort of thing.

Citrix XenServer is about a third of the cost of VMWare ESX so it may be worth you considering - I like it!

[dhicks]

I'm taking my first proper looks at Xen (it's free!).

My philosophy exactly :-) That's also why I used CentOS - basically Red Hat but free, too.

If I set up three servers, how do I get them to access the same LUN.

Pick a SAN technology, install the server on your central SAN hardware, install the client on your Xen machines, connect each client and away you go - i.e. install an iSCSI "target" (server) on a central computer with a fast network connection and a bunch of harddrives, install an iSCSI "initiator" (client) on each Xen processing machine, add an entry in each Xen machine's startup script or fstab to connect to the iSCSI target, done.

As far as I know, Red Hat / CentOS includes all the above built-in, just select the appropriate option at install time or simply pick the right package to install. Personally, I think SAN are better suited to larger enterprises, so I provide fail-over / live migration via block devices mirrored with DRBD - basically, each VM uses a block that is replicated in real time to a separate physical machine, so if one machine goes down you can simply switch over to the other one. It means you have to have double the storage capacity distributed around your servers, but you avoid having to buy any SAN hardware and you get the performance of a local harddrive.

Also can it do the equivalent of VMWares High Availability - so if server fails it auto restarts on one of the other servers?

The facility is there using Xen, although I haven't gotten around to sorting that out yet. You have to make sure that both Xen servers can write to the block device, which with DRBD involves setting up a block device that can be written by two machines at once, which sounds a bit more fiddly.

Finally, what software so you use to manage the servers/vm's?

I currently monitor virtual machines with my own script, but I plan to move to Enomalism at some point:

Enomaly : Elastic Computing (Clarity to Cloud Computing): Home

--
David Hicks

[DMcCoy]

Sun's xVM will be the way forward but they have not committed to a release date yet.

With Citrix XenServer Enterprise you get your XenMotion and a Windows Management console which are two things you seem to be after. For shared access to LUNs you allocate the LUNs to multiple servers and set the storage repositories up as lvmohba (LVM over HBA)... it's quite easy if you follow the instructions. There's also P2V utilities if you like that sort of thing.

Citrix XenServer is about a third of the cost of VMWare ESX so it may be worth you considering - I like it!

How much is Xen Enterprise with a years support?

[Ric_]

@DMcCoy: IIRC it's approx £1300 for year one and less there after... that's per server without a limitation on the number of processors (hence why I have 2x quad CPU servers rather than 3x dual CPU servers).

[tmcd35]

Not that far from VMWare then. From memory VI:3 Standard + 1yr support is £1600 - Edu discount per server.

[Ric_]

Not that far from VMWare then. From memory VI:3 Standard + 1yr support is £1600 - Edu discount per server.

However you have the limitation that licenses are for 2 CPUs and there is an additional charge of just over £1000 for the management server.

[tmcd35]

That's to Physical CPUs, not core count. In one of our ESX boxes we have two Xeon Quads (2 CPUs, 8 Cores).

So Does Xen Enterprise come with a management server equivalent at that price then?

[DMcCoy]

VI Enterprise is around £2100 at the moment, which is probably cheaper than getting VI Standard + VMotion now. The support is around £450 a year for Enterprise.

[Ric_]

That's to Physical CPUs, not core count. In one of our ESX boxes we have two Xeon Quads (2 CPUs, 8 Cores).

So Does Xen Enterprise come with a management server equivalent at that price then?

I have two quad CPU quad-core boxes so imagine the licensing!

The configuration data is stored across your 'resource pool' and there is a Windows management console for doing most tasks. Hence, no management server is needed.

Incidentally, the price I mentioned was for 'Enterprise' which gives you everything but 'Provisioning Server'.

[matt40k]

tmcd35, PM if you need any help with Xen.