<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; color: rgb(0, 0, 0); font-size: 14px; font-family: Calibri, sans-serif; "><div><p style="margin: 0px; font-family: Calibri; ">Hi.</p>
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<p style="margin: 0px; font-family: Calibri; ">I'm looking into reference architectures for OpenStack deployments for a project taking place soonish. I'm looking to build an OpenStack environment with an as yet undetermined (but might scale to thousands) compute core count. It'll most likely be based on 10GbE networking constructs. </p>
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<p style="margin: 0px; font-family: Calibri; ">I've been tasked with looking at backend storage architecture for the platform, as well as the bigger picture of how it'll all fit together – but first and foremost, there are a lot of guidelines and requirements for functionality and a minimum level of service I'd like to meet. One such minimum requirement is true live migration that my company has told me is a must from an availability perspective. </p>
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<p style="margin: 0px; font-family: Calibri; ">After looking over the majority of the documentation that I can find, it would seem to me, the path of least resistance here is to use a shared storage mechanism. I've read about two kinds of migration, one being block based, the other being "true" live. </p>
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<p style="margin: 0px; font-family: Calibri; ">I've talked to a few experienced openstack users and three of them suggest that the shared storage path is the sensible path for what we're undertaking, but I'd like to dig deeper here, as I've been given a lot of comments by others suggesting that such a platform or mechanism (shared storage array/SAN style architecture) isn't scalable – opting for local storage inter-node instead.</p>
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<p style="margin: 0px; font-family: Calibri; ">Personally, I'm not convinced of this entirely, and I perceive that with modern storage arrays and with some of the controller technology we have available to us now (think: extremely high performance controllers, inter-array tiering mechanisms including "hot" or "warm" SSD cache mechanisms) a shared storage methodology could work very well, be easier to manage and ultimately be a success.</p>
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<p style="margin: 0px; font-family: Calibri; ">I've been told by several people that if I used shared storage in an effort to get to a point where live migration is a possibility and is sane, I leave myself open to flooding the shared storage backend if I boot up lots of VM's at once and a lack of IO scalability because my storage is "bound" to what a storage array is capable of [so, to that end, growing it, scaling it and making it perform could be expensive], but, again, I'm not sure that's entirely true due to the significant caching that might take place internally.</p><p style="margin: 0px; font-family: Calibri; "><br></p><p style="margin: 0px; font-family: Calibri; ">I'm very interested in understanding what others have done here and how they have tackled such scenarios. </p><p style="margin: 0px; font-family: Calibri; "><br></p><p style="margin: 0px; font-family: Calibri; ">Thank you for your time, openstack list.</p><p style="margin: 0px; font-family: Calibri; "><br></p><p style="margin: 0px; font-family: Calibri; ">--z</p>
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