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Ideas for booting virtual machines on diskless nodes

Posted on 2008-06-21
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Last Modified: 2013-12-24
Hi,

I'm deploying a new hosting platform in the autumn, and we'd like to look at having a central storage device, which contains virtual machine images for a number of machines.  The physical machines would be diskless, and boot from LAN via PXE into the Xen or VMWare hypervisor.

Has anyone done this?  Can anyone point me at some decent documentation - I'm not quite certain of the best way to have persistent storage that's shared between multiple VMs, so am looking for ideas?  If it's not been done - why isn't it sensible, and what should be done instead?
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Question by:rtsh
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7 Comments
 
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by:agriesser
ID: 21839001
What would be the central storage device? Any ideas by now?
Why not boot directly from the central storage device (if possible)? It would be much faster and more failsafe than booting via PXE especially in virtualized environments because if the storage fails, the virtual machines fail too and therefore it's no drawback.

We'll implement an ESX cluster farm this autumn at our company using IBM or HP blade center servers booting off a Clariion CX600 attached via FibreChannel.
The test installation works perfectly fine so far.
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by:rtsh
ID: 21839022
Perhaps it's a lack of my understanding of SAN, but given that we need to have genuinely communal file shares, we thought that a SAN couldn't deliver this itself, but would need a front end to present the storage via some network protocol (eg NFS, CIFS), and given that was the case, we were considering storing the images on a NAS.  Perhaps this is only practical when, as is the case in our situation, the OS image and base data required for the server to function is relatively small, and so can fit in RAM.
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by:agriesser
ID: 21839038
If you're heading for ESX3i, you can get it installed even in flash memory of your server, but for ESX 3.5 you don't want to boot from PXE, believe me.
I don't even think that this setup is supported by VMware.

In any case, you will have to pull some hundreds of megabytes from the LAN for the server to even boot and you'll be wasting precious RAM for holding the filesystem data of the root filesystem.

As english is not my native language: Could you please rephrase the term "genuinely communal" for me? I think I don't get the point of this wording.
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by:rtsh
ID: 21839067
Ok. Maybe you can answer a slightly different question, which relates more to VMWare than the SAN side of things.  Are you booting a number of machines to run exactly the same VM disk image, or do you need one copy of the disk image per instance of the VM?
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by:agriesser
ID: 21839080
No, we don't do that currently, but we evaluated it and we were not satisfied because of the fact that if you want to create a VDI (Virtual Desktop infrastructure) environment (in your case it would rather be a VSI (Virtual Server Infrastructure) ) you will need N times the disk space you will need for a single VM and having a hundred VMs around with each of them having 10GB of system partitions sums up to 1TB of disk space just for the system partitions.

I once asked VMware if they're going to address this and they told me that they're just about to release this new feature (whatever it will be called). Using this new feature you can define a template disk where all your virtual machines boot from and only the differences to this template will be stored in separate files.

I haven't checked back since then, maybe this feature is already available in ESX 3.5 update 1.

Would that suite your needs?
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by:rtsh
ID: 21839097
Yeah - that's exactly what's required in our circumstances.  Thanks for your advice.  I'll contact our vmware rep and have another chat.

Are there any other tips that you'd care to share following your evaluation?
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agriesser earned 250 total points
ID: 21839109
Well, I don't know what else to say in particular.
There are so many things to consider when planning a virtual infrastructure... :)
I'd be happy to answer specific questions though, so if anything is unclear, drop me a line (or ask a question in here) and I'll see what I can do for you.
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