locked
Storage Spaces - Enclosure Awareness RRS feed

  • Question

  • Hi there,

    I've been tinkering aroud some time now to dig myself into Storage Spaces in Windows Server 2012 R2. There is one main thing that keeps me from understanding how to (hopefully) correctly plan and size a storage based on Storage Spaces: enclosure awareness.

    Planning Storage Spaces with one enclosure seems simple and there are many sources out there, that can give useful hints to the do's and don'ts, but when it comes to "more than one" enclosure, I generally find the following information in each and every whitepaper, forum, discussion, ...

    https://technet.microsoft.com/en-us/library/mt243829.aspx

    Maximum fault tolerance without disrupting virtual disks that have enclosure awareness enabled:

    Two-way mirror: Three enclosures --> Sustains one enclosure or one disk fail

    If I got it correctly, Storage Spaces will distribute blocks written to a two-way mirror with enclosure awareness to two (2) disks on different enclosures, right? So each and every block will reside on a disk in two different enclosures. Given only two enclosures would render each data block on each enclosure in a two-way mirror, I would assume. So why do I need three enclosures?

    I already found some hints to a solution, but I would like to understand the requirements instead of just accepting that this is the case ...

    • Some say, a Storage Space needs 50% + 1 Disk to stay online (which would not work with an even number ob enclosures), but why?
    • Others say, it has to do with the quorum of the SOFS and a split brain scenario (even if I don't want to implement SOFS?!?)

    I would really really like to understand, how this thing works under the hood. Can anyone drag me in the right direction, pleeeease?

    Regards,
    Marc

    Monday, October 26, 2015 9:37 AM

Answers

  • To understand windows storage ( keeping the fact that Microsoft is NOT a storage / hardware company), i would always read vendor documents which gives me good overiview of the technology.

    http://sp.ts.fujitsu.com/dmsp/Publications/public/wp-windows-storage-spaces-r2-performance-ww-en.pdf

    and the below videos are where i am learning to understand the internals

    https://channel9.msdn.com/Series/Storage-Spaces-Deep-Dive 

    • Proposed as answer by Mary Dong Friday, October 30, 2015 1:40 AM
    • Marked as answer by Mary Dong Thursday, November 5, 2015 2:08 AM
    Monday, October 26, 2015 12:58 PM

All replies

  • To understand windows storage ( keeping the fact that Microsoft is NOT a storage / hardware company), i would always read vendor documents which gives me good overiview of the technology.

    http://sp.ts.fujitsu.com/dmsp/Publications/public/wp-windows-storage-spaces-r2-performance-ww-en.pdf

    and the below videos are where i am learning to understand the internals

    https://channel9.msdn.com/Series/Storage-Spaces-Deep-Dive 

    • Proposed as answer by Mary Dong Friday, October 30, 2015 1:40 AM
    • Marked as answer by Mary Dong Thursday, November 5, 2015 2:08 AM
    Monday, October 26, 2015 12:58 PM
  • Hey Marc,

    Your initial theories are exactly on point as to why Storage Spaces requires 3 enclosures for a 2-way mirror.  The first point you have that Storage Spaces needs >50% of the PhysicalDisks to stay online is true and it's to prevent the split brain scenarios (which don't only apply to SOFS, but to Spaces as well).

    One simple example is:

    Imagine if there are 2 enclosures (same # of drives in each) and one enclosure goes down.  We'd hope everything will still run properly and files are saved.  Now on a reboot the enclosure doesn't power up but the first enclosure comes up, and more files are saved.  When both enclosure eventually come back up, we end up in a split brain scenario.

    In the example above, at all times, there was only 1 missing enclosure or data copy, but we don't know exactly how to resolve the mismatched data.  To be able to maintain the guarantee of having no issues with 1 enclosure completely failing, three enclosure are needed.

    I hope this helps point you in the right direction.

    Thanks,

    Alex

    Monday, November 16, 2015 11:55 PM