Storage Spaces - Disk resiliency RRS feed

  • Question

  • Hi,

    I'm testing Storage Space on Windows 2012 R2 at the moment and I'm a bit puzzled with disk redundancy.

    I have a server with 24 SATA disks attached through a JBOD controller (1 enclosure).
    I then create a storage pool across all 24 disks and create a two-way mirrored virtual disk on top of that.

    My understanding is that, when using a two-way mirror with 2 to 4 disk, only one disk can fail without impacting the virtual disk.
    If, however, the total disks increases to 5, 2 disks can fail.

    In my lab (24 disks), I would expect to, at the very least, be able to loose 2 disks without any impact, but unfortunately, that's not the case.
    As soon as I "fail" a second disk, the entire virtual disk goes down!

    This doesn't make any sense to me. Surely, with 24 disks, I should be able to sustain more disks failure without impacting the entire virtual disk?


    Friday, January 10, 2014 12:44 AM


All replies

  • If you run two-way mirror that means you have a two replicas of the same block on whole disk set. As Storage Spaces use comparably small (128MB AFAIK) chunk for interleaving data on Storage Spaces content gets scrambled between all the disks you have. If one drive fails it's OK but dual drive faulure takes away some chunks that belong to this drive only... Number of disks does not matter in this case.

    So basically everything works as expected. See:

    Mirror spaces are designed for increased performance and protect your files from drive failure by keeping more than one copy. Two-way mirror spaces make two copies of your files and can tolerate one drive failure, while three-way mirror spaces can tolerate two drive failures. 

    So if you need to have two drives fault tolerant config you need to go for either a three-way mirror or double parity set.

    Hope this helped :)

    StarWind VSAN [Virtual SAN] clusters Hyper-V without SAS, Fibre Channel, SMB 3.0 or iSCSI, uses Ethernet to mirror internally mounted SATA disks between hosts.

    • Marked as answer by _Stephane_MVP Tuesday, January 14, 2014 1:13 AM
    Friday, January 10, 2014 1:02 PM
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    Monday, January 13, 2014 12:51 PM
  • Hi,

    "Unfortunately" it looks like VR38DETT is correct indeed and you can only lose one disk per storage pool in the case of a two-way mirror.

    That answers my question.

    Thank you very much for your assistance,

    Tuesday, January 14, 2014 1:13 AM