Burned by Eschewing Best Practices
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@Brains said:
@Dashrender Yea its really crazy. Its because the HDD wrote date above the 137GB mark which it could not address
Basically the filesystem went out into no-man's land and corrupted.
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Another example. Minor, but again, best practices make life easy.
Beyond not understanding how some basics work (like thinking that the ILO needed an OS to work, which would defeat its purpose; and getting the name of the hardware wrong) he decided that he didn't want to virtualize and is trying to get modern Windows 2012 R2 onto a rather old HP Proliant DL360 G5. The hardware is perfectly viable but far older than HP is going to support for a modern OS with drivers. Had he virtualized like would have been sensible he would have never even known that there was a driver issue. His entire issue exists only because he avoided a simple best practice and then didn't think of switching to the best practice once he hit the roadblock caused by avoiding it.
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Here is a future case of Burned by Eschewing Best Practices in the making, Spiceworks Link
So far from the article the OP is looking for help with a renovated virtualization project, yet already has an IVPD on Xenserver, and wants to build a new IVPD on Hyper-V.
And "budget is not a concern" (which this really should be an article all on its own!)
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Not sure why? Can you summarise the IVPD article to explain why his solution is likely to see him burned? It looks like a waste of money, but if money is no object then I don't see why it's not a valid solution offering very high levels of uptime and reliability.
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@Carnival-Boy said:
Not sure why? Can you summarise the IVPD article to explain why his solution is likely to see him burned? It looks like a waste of money, but if money is no object then I don't see why it's not a valid solution offering very high levels of uptime and reliability.
lol, while it can provide very high levels of uptime and reliability, a two server software sync'ed solution should provide even higher of both.
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IVPD is generally a 3-2-1 system but it can scale as well.
Just because the scale increases in size, doesn't change the design of the system. Which is dependent on everything working to provide reliability.
If a SAN, switch, server, or any multiplicity of problems occurs the environment will be gimped. Effectively crippled to where recover-ability options will be extremely limited until all services are restored.
By adding more equipment, there is more complexity, with more complexity, more experience is required to support and maintain the systems. Which when something goes wrong, if an expert is not on-site (or immediately available) downtime and cost of said down time can sky rocket.
A much simpler approach (at least for what was "seen" in this topic) is a smaller footprint. With equipment that is capable of running independently of the other systems. For which everything can run on either system.
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@Carnival-Boy said:
Not sure why? Can you summarise the IVPD article to explain why his solution is likely to see him burned? It looks like a waste of money, but if money is no object then I don't see why it's not a valid solution offering very high levels of uptime and reliability.
IVPD - Inverted Pyramid of Doom. Sure you have two servers but they rely on a single storage subsystem. This is great and makes some things simpler in the long run... until you get to the point that hardware SANs are no more resilient then traditional servers, in fact they are traditional servers with some storage appliance software installed on top then sold for a massive profit. If you have dual SANs that makes it easier but you also have to look at the storage network in and of itself, do you also have dual switches, dual connections to both hosts, etc. This is a massive overhead in both budget and specialized skills.
In reality all of that work and money really doesn't make you any more reliable then having two physical hosts that have enough capacity to host the other's VMs when something goes wrong. Even more reliable in most cases. To get this even more reliable you could also forgo VM level replication and do everything at the application level.
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Two SANs offers a high degree of redundancy. I'm not sure where 3-2-1 fits in with that? He doesn't have a SPOF does he. He has redundant switches, redundant controllers, redundant SANs.
Sure there is complexity in there. But there's complexity with DAGs and file syncing as well.
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@Carnival-Boy said:
Two SANs offers a high degree of redundancy. I'm not sure where 3-2-1 fits in with that? He doesn't have a SPOF does he. He has redundant switches, redundant controllers, redundant SANs.
Sure there is complexity in there. But there's complexity with DAGs and file syncing as well.
Sure they do at what cost though? Is the cost worth it when you could get the same functionality for 10's of thousands of dollars less?
I've run into the dual controllers are totally going to save the world sales person before, which one of my former managers bought into. Turns out they share the same backplane and interaction with the drives. So when one controller locked up due to a firmware issue the other controller wouldn't take over. Everything went offline for ~8 hours until they overnighted us a new controller and we updated the firmware on both of them.
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Yeah, but cost isn't an issue as money is no object.
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@Carnival-Boy said:
Yeah, but cost isn't an issue as money is no object.
Any business that says that is just trying to fail! The whole point of a for profit company is to make money, and they should be doing so with smart spending.
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I'm not disagreeing, but if the OP says money is no object then you should treat that as fact. Maybe he has a magic money tree. Or is forced to spend a certain budget regardless of whether he needs it or not. Who knows, that's not the point. The point I'm trying to understand is why dual SANs and dual switches equals this pyramid of doom thing.
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It simply creates a larger pyramid, with more parts, which makes the entire system way more complex to troubleshoot, and fix should something happen.
It doesn't force the system to be less reliable when compared to the standard 3-2-1 model, as you are in fact creating a level of redundancy by implementing a 2nd SAN to backup the first.
But it's just wasteful in most cases.
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@DustinB3403 said:
It simply creates a larger pyramid, with more parts, which makes the entire system way more complex to troubleshoot, and fix should something happen.
It doesn't force the system to be less reliable when compared to the standard 3-2-1 model, as you are in fact creating a level of redundancy by implementing a 2nd SAN to backup the first.
But it's just wasteful in most cases.
Basically this. You aren't any more reliable then the dual host scenario and you've introduced several more layers of potential failure to your system.
There is a point where this makes sense... but not at 6 servers and two physical hosts. I'm not sure where the tipping point is but probably at the hundreds of virtual servers mark.
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@coliver said:
You aren't any more reliable then the dual host scenario and you've introduced several more layers of potential failure to your system.
You are actually mathematically substantially less reliable with that setup, at least from a hardware failure perspective.
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You got any facts to back that up? I find it extremely difficult to evaluate reliability. Anyway, you can't just judge it from a hardware failure perspective, since we're comparing hardware redundancy versus software redundancy (eg DAGs, file syncing). Both are complicated. Both require expertise to administer and both are risky.
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@Carnival-Boy said:
I'm not disagreeing, but if the OP says money is no object then you should treat that as fact.
I don't agree. Knowing someone is wrong, confused or doesn't understand something is exactly when they need help most, not the least. Tons and tons of what we do in IT is recognizing when people don't know what they need to know and helping them. In a case like this where we know they have to be wrong and don't understand what they are doing, should we really help them hurt themselves?
I totally get that this goes against my "always give people the benefit of the doubt" theory about never hurt the innocent to protect the guilty, but this is a case where money is never no object, it's simply not true, and it means someone desperately needs help and don't understand that they don't know.
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@Carnival-Boy said:
Or is forced to spend a certain budget regardless of whether he needs it or not. Who knows, that's not the point.
That would actually make money the ONLY object. Budget would be the whole concern, not just part of it.
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Well, ok, but the OP isn't' actually on ML so it's a moot point. What I'm really interested in is what the problem is with his solution (ignoring the financial cost) and why it is one of your inverted pyramid thingies. I'm not arguing, I just don't understand and want to learn.
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An IVPD looks stable and reliable when looking at it from the top, you have a bunch of equipment that supposedly will fail over between the devices.
But what isn't obvious from it, is if you look at it from the side you have individual layers of equipment, which is dependent on everything above or below its self.
So in the most simple example 3-2-1 you have 1 NAS(or SAN) 2 Switches and 3 Servers.
The name refers to three (this is a soft point, it is often two or more) redundant virtualization host servers connected to two (or potentially more) redundant switches connected to a single storage device, normally a SAN (but DAS or NAS are valid here as well.) It’s an inverted pyramid because the part that matters, the virtualization hosts, depend completely on the network which, in turn, depends completely on the single SAN or alternative storage device. So everything rests on a single point of failure device and all of the protection and redundancy is built more and more on top of that fragile foundation. Unlike a proper pyramid with a wide, stable base and a point on top, this is built with all of the weakness at the bottom. (Often the ‘unicorn farts’ marketing model of “SANs are magic and can’t fail because of dual controllers” comes out here as people try to explain how this isn’t a single point of failure, but it is a single point of failure in every sense.)
What this means is that there are so many potential points for failure, and that in the most basic approach of the 3-2-1 the "reliability" isn't at all reliable, or is only as reliable as your weakest link, which is often the NAS (or SAN).
Because if any part of that chain breaks the whole system can and likely will come crashing down. Here's a really good explanation from the one and only SAM
