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What are the different Consistency Point types and how are they measured?

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ontap-9
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perf
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Applies to

  • ONTAP 9
  • Data ONTAP 8
  • Data ONTAP 7

Answer

Consistency Points are measured using the sysstat command.

  • For more information on the options available and sample output, see the sysstat Manual Page.
  • The Consistency Point (CP) type is the reason for the CP that was started in the interval.
    • The first character in the CP Type column identifies the type of CP as listed below.
    • Multiple CPs display no cause character, just the count of CPs during the measurement interval.
    • The CP types are described as follows:

CP Type

Definition
'.' No CP started during the sampling interval
B Back to back CPs (CP generated CP)
b Deferred back to back CPs (CP generated CP)
D CP caused by a low number of datavecs (statics allocated buffer space for writes)
F CP caused by full NVLog; the amount of logged data in the storage system's NVRAM pool is high enough that it is ideal to start a CP to force it out to disk
H CP caused by high water mark; the amount of modified data in the storage system's memory cache is high enough that it is ideal to start a CP to force it out to disk
L CP caused by low watermark; the amount of memory available for routine housekeeping tasks is low enough that it is ideal to start a CP to release some more
M CP caused by low mbufs; writes data to the disk in order to prevent an out-of-memory buffer situation
N CP caused by the NV Log reaching a maximum number of entries
S CP caused by a snapshot operation
T CP caused by timer
U CP caused by flush; one or more clients who have been issuing asynchronous writes (that is, writes that under the rules of the client protocol do not have to be committed to persistent storage immediately) has issued a request that all of its outstanding uncommitted I/Os should now be committed to persistent storage
V CP caused by low virtual buffers
Z CP caused by internal sync; the storage system wants to force a disk update, usually during snapshot processing
: Continuation of CP from the previous interval
# Continuation of CP from the previous interval and the storage system has determined it needs to commit the current data to disk (a watermark of some sort has been reached) so that the next CP will be of type B
  • Only CP’s of type 'B' or 'b' will affect write latency.
  • The type character is followed by a second character which indicates the phase of the CP at the end of the sampling interval.
    • If the CP completed during the sampling interval, this second character will be blank.
    • The phases are as follows:
      • 0 Initializing
      • n Processing normal files
      • s Processing special files
      • f Flushing modified data to disk
      • v Flushing modified superblock to the disk
      • q Processing quota files  

Additional Information

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