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storage - ZFS over iSCSI high-availability solution

I am considering a ZFS/iSCSI based architecture for a
HA/scale-out/shared-nothing database platform running on wimpy nodes of plain PC
hardware and running FreeBSD 9.



Will
it work? What are possible
drawbacks?



Architecture




  1. Storage
    nodes have direct attached cheap SATA/SAS drives. Each disk is exported as a separate
    iSCSI LUN. Note that no RAID (neither HW nor SW), partitioning, volume management or
    anything like that is involved at this layer. Just 1 LUN per physical
    disk.


  2. Database nodes run ZFS. A ZFS
    mirrored vdev is created from iSCSI LUNs from 3 different storage
    nodes. A ZFS pool is created on top of the vdev, and within that a filesystem which in
    turn backs a database.


  3. When a disk or
    a storage node fails, the respective ZFS vdev will continue to operate in degraded mode
    (but still have 2 mirrored disks). A different (new) disk is assigned to the vdev to
    replace the failed disk or storage node. ZFS resilvering takes place. A failed storage
    node or disk is always completely recycled should it become available
    again.



  4. When a database node
    fails, the LUNs previsouly used by that node are free. A new database node is booted,
    which recreates the ZFS vdev/pool from the LUNs the failed database node left over.
    There is no need for database level replication for high-availability
    reasons.




Possible
Issues




  • How
    to detect the degradion of the vdev? Check every 5s? Any notification mechnism available
    with ZFS?


  • Is it even possible to
    recreate a new pool from existing LUNs making up a vdev? Any
    traps?


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