Skip to main content
NetApp Response to Russia-Ukraine Cyber Threat
In response to the recent rise in cyber threat due to the Russian-Ukraine crisis, NetApp is actively monitoring the global security intelligence and updating our cybersecurity measures. We follow U.S. Federal Government guidance and remain on high alert. Customers are encouraged to monitor the Cybersecurity and Infrastructure Security (CISA) website for new information as it develops and remain on high alert.
NetApp Knowledge Base

What is Consistency Point, and why does NetApp use it?

Views:
2,339
Visibility:
Public
Votes:
3
Category:
ontap-9
Specialty:
perf
Last Updated:

Applies to

  • ONTAP 9
  • Data ONTAP 8
  • Data ONTAP 7

Answer

  • A storage controller has two separate memory buffers for storing write data.
  • The size of these buffers is based on the amount of non-volatile RAM (NVRAM) in a given system.
  • This can be calculated as 1/2 the NVRAM size for stand-alone systems, 1/4 the NVRAM size for clustered systems, and 1/8 the NVRAM size for 4/8-node MetroClusters.
  • All writes into a storage controller are stored concurrently in the following locations:
    • Local memory buffer
    • Local NVRAM/NVMEM
    • Remote NVRAM (Clustered systems only)
    • Remote NVRAM of the DR partner (MetroCluster systems only)
  • As soon as the process to log to NVRAM is confirmed, the controller acknowledges the write as completed to the client machine (app, protocol?).
  • At pre-defined triggers, this buffered write data is processed from the storage controller memory through the Write Anywhere File Layout (WAFL) and RAID layers and written to disk.
  • The active file system pointers on the disk are not updated to point to the new locations until a write is completed.
  • Upon completion of a write to disk, the contents of NVRAM are cleared and made ready for the next batch of incoming write data.
    • This act of writing data to disk and updating active file system pointers is called a Consistency Point (CP).
  • During the writing phase of one memory buffer, the second memory buffer and NVRAM space ( both local and remote ) are used to store and acknowledge incoming writes.

Additional Information

additionalInformation_text

 

Scan to view the article on your device