Xenserver and Storage

scottalanmiller

The technologies you list all have their pros and cons, so knowing what these are is what I really need to know. How do they handle a node failure? Out of sync data etc? How easy are they to implement? How much do they roughly cost?

That's kind of the point. VSAN vs. Native vs. VSA and RAID vs. RAIN do have pros and cons, but they are trivial and under the hood. They are background noise, a distraction. What matters to you (or to anyone) is actual, real world implementations and what is available, not how it works. For example, Starwind uses VSAN and Network RAID, but if they use VSA and RAIN, you'd not care at all. All you care about is the resulting performance, scale, reliability and cost. Does that make more sense?

So for you, it all comes down to actual products and how they meet your needs, not how they are doing that job.

scottalanmiller

I hate to say it, because I love Xen, but it might really be worth leaving Xen behind. The solutions for it are few and far between and often rather complicated. KVM or Hyper-V have what you want, for free, from Starwind done in a really good way for what you need. And if you need or want support, you have that option from them. And they are active here, as well. So loads of choices.

scottalanmiller

Going with Xen, you are far more limited to just a few options. With raw Xen, you have more options. With XenServer, they specifically remove or disallow certain common solutions like DRBD.

olivier

DRBD is working with XS via HA Lizard, XOSAN coming in stable soon, people also working on Ceph (don't know the progress on this one, won't be hyperconvergence however).

I'm not sure there is a ton of solution for a 2 node setup anyway. Even in VMWare (you need a "witness appliance" which is basically the arbiter node of Gluster).

Maybe I missed something?

scottalanmiller

@olivier said in Xenserver and Storage:

DRBD is working with XS via HA Lizard, XOSAN coming in stable soon, people also working on Ceph (don't know the progress on this one, won't be hyperconvergence however).

So one that has been known to not be very good and two that aren't out yet. Seems like that kind of answers that. Xen has a future, but not a present. Nothing wrong with that. But he needs to deploy today.

scottalanmiller

@olivier said in Xenserver and Storage:

I'm not sure there is a ton of solution for a 2 node setup anyway. Even in VMWare (you need a "witness appliance" which is basically the arbiter node of Gluster).

No one is considering VMWare, but no one needs three nodes. VMware, Hyper-V and KVM all have Starwind and other options, at two nodes.

olivier

XOSAN is just weeks from release

How Starwind deals with split brain in 2 nodes scenario? Why it would be better than VSAN? (which is somehow a leader in the VMWare market itself IIRC)

edit: those are true questions, not rhetorical. I'm curious about how to deal with some cases in 2 nodes.

scottalanmiller

@olivier said in Xenserver and Storage:

How Starwind deals with split brain in 2 nodes scenario? Why it would be better than VSAN? (which is somehow a leader in the VMWare market itself IIRC)

I wouldn't use the term VSAN as that is a generic word (like SAN) and both Starwind's and VMware's solutions are called VSAN So which is better, VSAN or VSAN?

Starwind has done a lot of work to deal with split brain management with two nodes, VMware has not. Starwind is in the business of making things cost effective and focusing on small shops. VMware is in the business of selling sprawl and focusing on large customers. VMware's smallest purchase increment is three nodes. So they have totally different intended user bases and purposes. VMware deals with split brain the easy way, but having a witness node at all times. This can just be on a desktop, though, it need not be anything hard core. Starwind simply has a lot more intelligence under the hood to arbitrate a scenario where both nodes are alive but severed.

Starwind has the pretty massive advantage of being free, running on free products, and bring vendor agnostic. VMware VSAN is not free, requires more nodes, runs only on expensive products, and is vendor locked in.

olivier

I would be curious to understand how it's possible to deal with a replication link failure in 2 nodes scenario. I don't see a lot of options:

you stop writes to avoid split brain
you write data in both nodes but if you have one LUN for mutliple VMs, you are doomed to discard one node data

Do you have more details or documentation on how it works?

scottalanmiller

Best to have @KOOLER explain the mechanism, I don't want to get that part wrong.

olivier

And in short, because Starwind doesn't support XenServer, you think it's better to discard XenServer Why not, maybe in 2 nodes scenario it's an acceptable point of view ^^

scottalanmiller

@olivier said in Xenserver and Storage:

And in short, because Starwind doesn't support XenServer, you think it's better to discard XenServer Why not, maybe in 2 nodes scenario it's an acceptable point of view ^^

What's the other option? HA-Lizard is only available for two nodes. Nothing else is on the market. Starwind, like everyone else, is expected to have something out for Xen in the future, but no one seems to have solutions today. DRBD does work, but isn't ideal and XenServer specifically disavows it. Leaving a weird situation where we can come up with solutions, but we lack elegance or support. When switching out Xen seems to be the obvious solution making all of this moot.

scottalanmiller

HP VSA might have been available on Xen, but they've pulled it.

olivier

@scottalanmiller said in Xenserver and Storage:

@olivier said in Xenserver and Storage:

And in short, because Starwind doesn't support XenServer, you think it's better to discard XenServer Why not, maybe in 2 nodes scenario it's an acceptable point of view ^^

What's the other option? HA-Lizard is only available for two nodes. Nothing else is on the market. Starwind, like everyone else, is expected to have something out for Xen in the future, but no one seems to have solutions today. DRBD does work, but isn't ideal and XenServer specifically disavows it. Leaving a weird situation where we can come up with solutions, but we lack elegance or support. When switching out Xen seems to be the obvious solution making all of this moot.

2 node isn't the objective? So why discard that option?

scottalanmiller

@jrc said in Xenserver and Storage:

So currently I have 2 HP servers that are being used and XenServer hosts.

It is kind of the objective from what I am seeing. It may not be THE objective, but other solutions require buying an unnecessary extra server just to have a third, so that's a pretty big negative.

Changing from Xen to KVM or Hyper-V is free and generally trivial. Adding 50% hardware overhead to make XenServer work is not. So take any reaction you had to moving off of Xen and magnify that by a few orders of magnitude for the equivalent reaction to adding more hardware to fix Xen-ecosystem shortcomings.

scottalanmiller

@olivier said in Xenserver and Storage:

@scottalanmiller said in Xenserver and Storage:

@olivier said in Xenserver and Storage:

And in short, because Starwind doesn't support XenServer, you think it's better to discard XenServer Why not, maybe in 2 nodes scenario it's an acceptable point of view ^^

What's the other option? HA-Lizard is only available for two nodes. Nothing else is on the market. Starwind, like everyone else, is expected to have something out for Xen in the future, but no one seems to have solutions today. DRBD does work, but isn't ideal and XenServer specifically disavows it. Leaving a weird situation where we can come up with solutions, but we lack elegance or support. When switching out Xen seems to be the obvious solution making all of this moot.

2 node isn't the objective? So why discard that option?

Not discarded, just... absurd?

olivier

I don't see the logical connection. Right now, he owns 2 hosts, XS can work with HA lizard or XOSAN in few weeks. No need to buy extra hardware. That's an option. Not maybe a perfect option, but it's not an absurd one.

I don't understand why you are speaking about a 50% hardware overhead to make XenServer work.

I didn't know about the potential 2 nodes capability of StarWind (I still need to understand how ), so the only absurd thing is to make me tell stuff I never said

matteo nunziati

@olivier

I didn't know about the potential 2 nodes capability of StarWind (I still need to understand how )

Me too! (Again Not rethoric)

scottalanmiller

@olivier said in Xenserver and Storage:

I didn't know about the potential 2 nodes capability of StarWind (I still need to understand how ), so the only absurd thing is to make me tell stuff I never said

You asked why adding extra nodes wasn't an option. So I answered.

scottalanmiller

@olivier said in Xenserver and Storage:

I don't see the logical connection. Right now, he owns 2 hosts, XS can work with HA lizard or XOSAN in few weeks. No need to buy extra hardware. That's an option. Not maybe a perfect option, but it's not an absurd one.

Right, and we covered, a few times I thought, that HA-Lizard really isn't up to snuff and not all that viable. So we can't keep repeating that as an excuse for things working.

XOSAN we can evaluate when it is on the market and tested.

So again, at this time, didn't we just come back to "no solutions today on Xen"?