Xenserver and Storage
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@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.
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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?
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Best to have @KOOLER explain the mechanism, I don't want to get that part wrong.
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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 ^^ -
@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.
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HP VSA might have been available on Xen, but they've pulled it.
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@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?
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@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.
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@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?
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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 
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I didn't know about the potential 2 nodes capability of StarWind (I still need to understand how
)Me too! (Again Not rethoric)
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@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.
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@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"?
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@scottalanmiller said in Xenserver and Storage:
@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.
No, maybe I wasn't clear (EN not my main language).
You said: HA Lizard is only available for 2 nodes.
I answered that's exactly what he wanted (2 nodes) so why discarding HA lizard? -
@scottalanmiller said in Xenserver and Storage:
@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"?
I personally don't like solutions that doesn't scale, but if he want to stick on 2 hosts, that's an option. People said it works when it's backed with support. I never heard nor bad or good stories about it. So I wouldn't discard it just after one or two people saying something here. Maybe you have a better knowledge on HA Lizard community and feedback of users? I don't.
Regarding XOSAN, it's already available to test since 6 months and commercial release is in just weeks.
I just said you are really prompt to discard options but again I can be mistaken because I don't have the deep knowledge on HA Lizard community. And again, I wasn't aware of 2 node capability of Starwind.
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@olivier said in Xenserver and Storage:
I personally don't like solutions that doesn't scale,
Me too, one of the reasons that I like Starwind is that it is amongst the largest scaling solutions on the market. It is limited by the hypervisor limits, not its own.
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@olivier said in Xenserver and Storage:
I just said you are really prompt to discard options but again I can be mistaken because I don't have the deep knowledge on HA Lizard community. And again, I wasn't aware of 2 node capability of Starwind.
It's not me discarding HA-Lizard. The community has worked with it a bit and as a community, the general consensus has been that it just isn't stable enough to use (and doesn't scale.) I'm just repeating a concensus to you. If you feel I'm dismissing things out of hand, it is the community, not me, that you are speaking to. I'm just explaining to you why it is viewed that way.
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That's why I asked if you have better knowledge of community on this solution because I really don't. So if it's the case, that it's not stable (darn, it's here since a long time!), that's indeed not an option.
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@olivier said in Xenserver and Storage:
That's why I asked if you have better knowledge of community on this solution because I really don't. So if it's the case, that it's not stable (darn, it's here since a long time!), that's indeed not an option.
I only know what people have been seeing. Part of the inherent downside to it is that it is specifically "forbidden" by XenServer as it is DRBD. So while it is fine to do, you have to accept that you are going against the closest thing that XS has to a primary vendor. Which doesn't bother me, I would never, ever call Citrix for help on XS. But for most shops, that's a show stopper.
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@olivier said in Xenserver and Storage:
That's why I asked if you have better knowledge of community on this solution because I really don't. So if it's the case, that it's not stable (darn, it's here since a long time!), that's indeed not an option.
Issue with HA lizzard is that it doesn't have a stateful quorum system (just pinging a single IP address). You can split brain it.
