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Oracle® ZFS Storage Appliance Analytics Guide |
Chapter 3 Statistics and Datasets
Determining the impact of a dynamic statistic
Capacity: Capacity Percent Used
Capacity System Pool Bytes Used
Capacity: System Pool Bytes Used
Capacity System Pool Percent Used
Capacity: System Pool Percent Used
Data Movement NDMP Bytes Statistics
Data Movement: NDMP Bytes Statistics
Data Movement NDMP Operations Statistics
Data Movement: NDMP Operations Statistics
Data Movement Replication Bytes
Data Movement: Replication Bytes
Data Movement Replication Operations
Data Movement: Replication Operations
Data Movement Shadow Migration Bytes
Data Movement: Shadow Migration Bytes
Data Movement Shadow Migration Ops
Data Movement: Shadow Migration Ops
Data Movement Shadow Migration Requests
Data Movement: Shadow Migration Requests
Protocol Fibre Channel Operations
Protocol: Fibre Channel Operations
Protocol: HTTP/WebDAV Requests
Data Movement NDMP Bytes Transferred to/from Disk
Data Movement: NDMP Bytes Transferred to/from Disk
Data Movement NDMP Bytes Transferred to/from Tape
Data Movement: NDMP Bytes Transferred to/from Tape
Data Movement NDMP File System Operations
Data Movement: NDMP File System Operations
Data Movement Replication Latencies
Data Movement: Replication Latencies
Disk ZFS Logical I/O Operations
Disk: ZFS Logical I/O Operations
Memory Kernel Memory Lost to Fragmentation
Memory: Kernel Memory Lost to Fragmentation
The L2ARC is the 2nd Level Adaptive Replacement Cache, and is an SSD based cache that is accessed before reading from the much slower pool disks. The L2ARC is currently intended for random read workloads. This statistic shows L2ARC accesses if L2ARC cache devices are present, allowing its usage and performance to be observed.
When investigating performance issues, to check how well the current workload is caching in the L2ARC.
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As described in Overhead, breakdown such as by file name would be the most expensive to leave enabled.
To investigate L2ARC misses, check that the L2ARC has grown enough in size using the Advanced Analytic Cache L2ARC size. The L2ARC typically takes hours, if not days, to warm up hundreds of Gbytes when feeding from small random reads. The rate can also be checked by examining writes from Cache L2ARC I/O bytes. Also check the Advanced Analytic Cache L2ARC errors to see if there are any errors preventing the L2ARC from warming up.
Cache ARC accesses by L2ARC eligibility can also be checked to see if the data is eligible for L2ARC caching in the first place. Since the L2ARC is intended for random read workloads, it will ignore sequential or streaming read workloads, allowing them to be returned from the pool disks instead.
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