EMC/VMWare VAAI (VStoarge API for Array Integration)

• VAAI (vStorage API for Array Integration) is EMC/VMWare API that allows a hardware array to expose certain features of the array.
• The hardware array typically offers hardware acceleration for certain operations, including:
  • Clone Blocks/ XCOPY because intra-array copy is faster than through the host.
  • Zero Blocks/ Write same
  • Block delete
  • Atomic test and Set, used on VMFS volume
  • Thin provisioning
  • Native snapshot support
• Storage array should support hardware acceleration through VAAI.

Ceph and VAAI

• ESXi data store need storage array with a iSCSI interface.
• All ESXi writes are sync writes
• Ceph has a block device solution that is RBD (RADOS Block Device). This block device can act as back end to an iSCSI front end.
• iSCSI front end could be:
  • TGT (Linux SCSI target framework)
    • Mostly, userspace code is needed for iSCSI.
    • Not VAAI compliant
  • LIO (Linux IO)
    • VAAI compliant
  • SCST
  • NFS
• ESXi operations like consolidating snapshots/storage vmotion/cloning use 64kb IO’s. Assuming latency of 4ms for an operation, 1/0.004 =250 iops 64kb*250 = 16MB/s
• IO from VM’s will be passed through to Ceph at whatever size it is submitted as.

Resources

1. http://lists.ceph.com/pipermail/ceph-users-ceph.com/2015-July/003179.html
2. http://linux-iscsi.org/wiki/VStorage_APIs_for_Array_Integration
3. http://geekfluent.com/2012/03/26/what-will-vaai-v2-do-for-you-part-2-of-2-nfs/
4. https://www.spinics.net/lists/ceph-devel/msg29124.html