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What is the FlexVol read or write path?

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Applies to

ONTAP 9

Answer

Reads
  1. The read request comes into the NIC.
  2. The Network layer reads the data off of the NIC.
    • ONTAP internal latency counters start here.
  3. The request is sent to the Data layer of the node hosting the volume.
    • Put another way, the Data node is the one which has the disks of the volume.
  4. Data is checked from memory for completeness.
  5. If data is not in memory, it is pulled from cache then disk.
  6. The read is completed.
  7. The read is sent to the Network layer.
    • ONTAP internal latency counters stop here.
  8. The NIC sends the traffic back to the client.
Writes
  1. The write request comes into the NIC.
  2. The Network layer reads the data off of the NIC.
    • ONTAP internal latency counters start here.
  3. The request is sent to the Data layer of the node hosting the volume.
    • Put another way, the Data node is the one which has the disks of the volume.
  4. The write sits buffered in memory.
  5. Details of the write are written to NVRAM, and the HA partner's NVRAM if applicable.
    • This is for crash consistency purposes only.
    • The write is considered done only after writes to NVRAM and the HA partner's NVRAM complete.
  6. The write is completed.
  7. The write is sent to the Network layer.
    • ONTAP internal latency counters stop here.
  8. The NIC sends the traffic back to the client.

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