Someone doesn't like local storage for large amounts of data
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To recap:
- For XenServer SR (aka VM disks): local storage or remote storage, doesn't really matters, because we always have the ability to migrate the VDIs when needed
- Having large VDIs will reduce this flexibility. So it's better to use small VDIs and use NAS/SAN for mounting large space filled with a lot or big files.
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@Dashrender said in Someone doesn't like local storage for large amounts of data:
As those who have been around ML for a while know, the general consensus around here is to use local storage for your VM workloads when possible.
He still is. He didn't move from using local, nor from VMs on local. He's talking about file servers he recommends a NAS instead of a file server.
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@olivier said in Someone doesn't like local storage for large amounts of data:
- Having large VDIs will reduce this flexibility. So it's better to use small VDIs and use NAS/SAN for mounting large space filled with a lot or big files.
That doesn't really make sense because NAS or SAN have all the same (or more) limitations in failing over large workloads as local storage does. It just introduces more overhead and risk having the extra equipment.
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Yes, whatever how you name it, but a physical appliance/machine which will serve a large bunch of files.
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@olivier said in Someone doesn't like local storage for large amounts of data:
@Dashrender said in Someone doesn't like local storage for large amounts of data:
Hmm... this flies in the face of hundreds if not thousands of posts on this forum.
That's my opinion, I don't care if it's shared or not. That's what I can see on the field. I won't create VMs with disks of hundreds of GBs. Or without knowing the pain it will cause if there is any operation to do on this VM (migration, backup, restore, whatever)
So this is all worded strangely because of the OP. Basically you are advocating physical storage devices instead of virtual, nothing more than that.
Problem is... all of those migration, backup, restore, etc. operations don't improve by going physical. They just don't get as many advantages going virtual. That large file servers aren't the best virtualization targets is accepted. That they don't still benefit from being virtual, though, is what is disputed. You've listed why virtual not better by as large of a margin as normal, but is any downside in play? Or simply not as overwhelmingly any upsides?
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@scottalanmiller I don't agree and that's not my point either. If a filer is overcrowded, that's not a virt vs physical issue, that's a capacity planning issue.
Here, I'm talking about general architecture, not implementation details.
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@olivier said in Someone doesn't like local storage for large amounts of data:
Yes, whatever how you name it, but a physical appliance/machine which will serve a large bunch of files.
But why not virtualize that one machine to get the benefits of virtualization? What's the advantage to giving up the extra benefits?
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@olivier said in Someone doesn't like local storage for large amounts of data:
@scottalanmiller I don't agree and that's not my point either. If a filer is overcrowded, that's not a virt vs physical issue, that's a capacity planning issue.
Here, I'm talking about general architecture, not implementation details.
It's physics. NAS and SAN are just local storage themselves. They have no magic. Anything they can do to aid failover, local storage can do without the extra overhead.
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@scottalanmiller What's the point of a virtual filer if you can't easily move it. Very large VDIs defeats the flexibility of virtualization.
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@scottalanmiller I think there is a misunderstanding somewhere, I don't get your point. I'm not talking about performances limits at all.
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@olivier said in Someone doesn't like local storage for large amounts of data:
@scottalanmiller What's the point of a virtual filer if you can't easily move it. Very large VDIs defeats the flexibility of virtualization.
Not at all, because those are "icing" benefits, not the cake benefits. Being able to move things isn't the core value in virtualization. And even if so, you are just saying why it isn't overwhelmingly better, but not saying why physical is better. If advocating physical, what is the actual benefit?
http://www.smbitjournal.com/2012/11/virtualization-as-a-standard-pattern/
http://www.smbitjournal.com/2015/04/virtualizing-even-a-single-server/
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Okay, let's imagine your NAS is on a larger VMs talking all space of your local storage of your XenServer/ESXi/whatever host. And exposing mounts to all other VMs on other hosts. That's doable but that's not my point. For me, this setup is almost the same of having a physical NAS/SAN.
My point is: for ALL your VMs, it's better to have smaller VDIs everywhere and mount a filer elsewhere if needed.
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By the logic that big VDIs defeat the purpose of virtualization because they cannot be moved, that also would undermine the accepted best practice of virtualizing when you have only a single physical server, but as we know you would always do that and the benefits are myriad even without that one benefit.
Things like driver stability, standard environments, snapshotting from outside of the OS, greater flexibility to combat the unknown, etc. are big deals.
And remember, you are only saying that you can't move the VDI as easily, but by going to physical it because "can't move it at all." Doing something in a difficult way is still easier than not being able to do something at all. So virtual still benefits from it, just not as much.
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@olivier said in Someone doesn't like local storage for large amounts of data:
Okay, let's imagine your NAS is on a larger VMs talking all space of your local storage of your XenServer/ESXi/whatever host. And exposing mounts to all other VMs on other hosts. That's doable but that's not my point. For me, this setup is almost the same of having a physical NAS/SAN.
Sure, ALMOST the same, but still a little better. That's the point. The VM approach still has benefits, the NAS is still a little worse. Why opt for worse when better is free?
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@scottalanmiller That's not my point. A big virtualized NAS is doable if you like. I was talking about the architecture. Damn, I have the impression to speak Chinese. Sorry if I can't express clearly my ideas in English.
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@olivier said in Someone doesn't like local storage for large amounts of data:
@scottalanmiller I was talking about the architecture.
Do you mean that if you have massive file serving needs that it makes the most sense to have that on unique hardware that is then shared to other VMs? That makes sense, but seems like a standard capacity algorithm solution rather than a special case. Any workload that becomes dramatically unbalanced from the others would operate in that way.
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@scottalanmiller Because that's not my point aaarrrgghh. I don't care, that's a not something I wanted to focus in my opinion at the first place.
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I think that we are all lost at this point. Maybe start over and word it fresh. What @Dashrender had in the original post was not at all what you had said.
I thought that you meant physical file server was better than a virtual one, but that wasnt it either.
I don't know what was originally said that prompted the conversation so only working from what is in the thread.
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The thing, initially, was about having VMs with large VDIs. Which is for me not a good practice.
But if you need to store a large amount of data, it's better to connect to a remote file share in the VM and keep small system disks (excepts for db/web usage, which are not huge in general).
That's all.
edit: is it more clear now?
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@olivier said in Someone doesn't like local storage for large amounts of data:
The thing, initially, was about having VMs with large VDIs. Which is for me not a good practice.
But if you need to store a large amount of data, it's better to connect to a remote file share in the VM and keep small system disks (excepts for db/web usage, which are not huge in general).
That's all.
edit: is it more clear now?
Let's see if I reword it correctly....
If your VM needs a lot of file storage.... then it is better to mount that from a file server rather than keeping it in the original VM?
