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[Tom Fifield <938365@xxxxxxxxxxxxxxxxxx>]

Thanks Yogesh!

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https://bugs.launchpad.net/bugs/938365

Title:
  Docs: Lack of OpenStack storage concepts explanation

Status in OpenStack Manuals:
  In Progress
Status in OpenStack Book for Ubuntu:
  In Progress

Bug description:
  The problem:
  I'm new to OpenStack and while learning it, many of it's concepts seem alien.

  I did read start guide PDF (Nova), the Install Guide (Nova) and parts of the Admin Guide (Nova).
   (from docs.openstack.org), but it doesn't explain the most basic concepts.

  Things like:
  1. Object Storage (swift) vs. Network File System (NFS)
  =============================================
  Why SWIFT ?

  According to: "notmyname"
  <notmyname> technologov: the things that object storage in general
  (and swift specifically) provides is large scale, cheap, and durable
  storage

  <notmyname> technologov: object storage is all about relaxing some of
  the constraints of a posix-style system. for example, if you don't
  have to provide atomic operations (ie you can rely on eventual
  consistency), you can much more easily scale a storage system and not
  have a central point of failure

  Also:
  I have seen a video, that explains a bit about hashing searches, but
  very incomplete.
  Also what happens if new servers get added or removed ?
  Such concepts need to be added into the docs.

  Does Object Storage also stores files ? (seems yes)

  How is SWIFT coherent ? Or it does not guarantee coherency ?

  2. Nova-volume vs Nova-object vs Images (glance) vs. Object Storage (swift)
  =============================================

  Both (1) Nova-volume and (2) Nova-object and (3) glance and (4) swift seem capable of
  storing VM hard disks.
  What's the conceptual difference between the three ?

  Possible Answer:
  "<notmyname> technologov: nova-volume is for block storage attached to
  a VM. glance is to manage the VM images in a nova cluster and provide
  nice ways of storing them (a bridge to the storage, not the storage
  itself). swift is an object storage system that can be used by glance
  or on its own. swift isn't a filesystem, so it's not "mountable" like
  the devices managed with nova-volume"

  Arguments & Discussion:
  <technologov> come on... "mountable" term is a joke... nowadays you
  can mount GMail or Wikipedia... via FUSE
  <technologov> w.p. is not a Filesystem either :)

  <notmyname> ok, so you don't use swift like a traditional hard drive.
  the only access to it is API-based (and the API is http)
  <notmyname> that can be wrapped into a FUSE filesystem (but there are
  big tradeoffs in doing so--advantages too, of course)

  Once we can agree on the concepts, need to patch official docs.

  =======================================================
  Some users say this is like Amazon AWS or Amazon S3 or whatever...

  the problem is: I have never used Amazon. I have used RHEV (Red Hat
  Enterprise Virtualization), which is based on local storage or NFS or
  iSCSI concepts... All the "object storage" concepts are 100% brand new
  to me.

  We need to define the concepts, and make sure they are understandable
  for all users alike from different backgrounds.

  -Technologov, 22.02.2012.

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