eG Monitoring
 

Measures reported by ClariionCacheTest

A cache is a temporary storage area where frequently accessed data can be stored for rapid access. Once the data is stored in the cache, it can be used in the future by accessing the cached copy rather than re-fetching or recomputing the original data.

This test monitors the current state, size, and usage of the read and write caches supported by the storage system.

The measures made by this test are as follows:

Measurement Description Measurement Unit Interpretation
Read_hit_ratio Indicates the percentage of read requests to this LUN that were serviced by the cache. Percent Ideally, the value of this measure should be high. A low value indicates that many read requests are serviced by direct disk accesses, which is a more expensive operation in terms of processing overheads.
Write_hit_ratio Indicates the percentage of write requests to this LUN that were serviced by the cache. Percent Ideally, the value of this measure should be high. A low value indicates that many write requests are serviced by direct disk accesses, which is a more expensive operation in terms of processing overheads.
Dirty_cache_pages Indicates the number of dirty cache pages. Number  
Dirty_cache_pages_owned Indicates the number of cache pages owned. Number  
SPA_read_cache_state Indicates the current state of the read cache for Storage Processor (SP) A.   If the read cache of the storage processor (SP) A is enabled, then this measure will report the value Enabled. If not, then, this measure will report the value Disabled.

The numeric values that correspond to each of the states discussed above are available in the table below:

Numeric Value State
1 Enabled
0 Disabled

Note:

By default, this measure reports the values Disabled or Enabled to indicate the status of the read cache. The graph of this measure however, represents the cache status using the numeric equivalents - 0 or 1.
SPA_write_cache_state Indicates the current state of the write cache for Storage Processor (SP) A.   If the write cache of the storage processor (SP) A is enabled, then this measure will report the value Enabled. If not, then, this measure will report the value Disabled.

The numeric values that correspond to each of the states discussed above are available in the table below:

Numeric Value State
1 Enabled
0 Disabled

Note:

By default, this measure reports the values Disabled or Enabled to indicate the status of the write cache. The graph of this measure however, represents the cache status using the numeric equivalents - 0 or 1.
SPA_cache_pages Indicates the total number of pages in the cache of Storage Processor A. Number For best performance, each Storage Processor (SP) should have the maximum amount of its memory in cache and should use the default settings for the cache properties. Therefore, ideally the number of memory pages in the cache should be high.
SPA_read_cache_size Indicates the current size of the read cache of Storage Processor A. MB The read cache holds data that is expected to be accessed in the near future. If a request for data that is in the cache arrives, the request can be serviced from the cache faster than from the disks. Each request satisfied from cache eliminates the need for a disk access, reducing disk load. If the workload exhibits a "locality of reference" behavior, where a relatively small set of data is accessed frequently and repeatedly, the read cache can improve performance. In read-intensive environments, where more than 70 percent of all requests are reads, the read cache should be large enough to accommodate the dataset that is most frequently accessed. For sequential reads from a LUN, data that is expected to be accessed by subsequent read requests is read (prefetched) into the cache before being requested. Therefore, for optimal performance, the read cache should be large enough to accommodate prefetched data for sequential reads from each LUN.
SPA_write_cache_size Indicates the current size of the write cache of Storage Processor A. MB Write cache serves as a temporary buffer where data is stored temporarily before it is written to the disks. Cache writes are far faster than disk writes. Also, write-cached data is consolidated into larger I/Os when possible, and written to the disks more efficiently. (This reduces the expensive small writes in case of RAID 5 LUNs.) Also, in cases where data is modified frequently, the data is overwritten in the cache and written to the disks only once for several updates in the cache. This reduces disk load. Consequently, the write cache absorbs write data during heavy load periods and writes them to the disks, in an optimal fashion, during light load periods. However, if the amount of write data during an I/O burst exceeds the write cache size, the cache fills. Subsequent requests must wait for cached data to be flushed and for cache pages to become available for writing new data. It is hence imperative that you rightly size the write cache.
SPA_free_mem_size Indicates the amount of physical memory of storage processor A that is currently unused. MB  
SPA_sys_buf Indicates the size of the system buffer of storage processor A. MB  
SPA_phy_sys_mem Indicates the total physical memory of storage processor A. MB  
SPB_read_cache_state Indicates the current state of the read cache of storage processor B.   If the read cache of the storage processor (SP) B is enabled, then this measure will report the value Enabled. If not, then, this measure will report the value Disabled.

The numeric values that correspond to each of the states discussed above are available in the table below:

Numeric Value State
1 Enabled
0 Disabled

Note:

By default, this measure reports the values Disabled or Enabled to indicate the status of the read cache. The graph of this measure however, represents the cache status using the numeric equivalents - 0 or 1.
SPB_write_cache_state Indicates the current state of the write cache of storage processor B.   If the write cache of the storage processor (SP) B is enabled, then this measure will report the value Enabled. If not, then, this measure will report the value Disabled.

The numeric values that correspond to each of the states discussed above are available in the table below:

Numeric Value State
1 Enabled
0 Disabled

Note:

By default, this measure reports the values Disabled or Enabled to indicate the status of the write cache. The graph of this measure however, represents the cache status using the numeric equivalents - 0 or 1.
SPB_cache_pages Indicates the number of pages read cache of storage processor B. Number For best performance, each Storage Processor (SP) should have the maximum amount of its memory in cache and should use the default settings for the cache properties. Therefore, ideally the number of memory pages in the cache should be high.
SPB_read_cache_size Indicates the current size of the read cache of Storage Processor B. MB The read cache holds data that is expected to be accessed in the near future. If a request for data that is in the cache arrives, the request can be serviced from the cache faster than from the disks. Each request satisfied from cache eliminates the need for a disk access, reducing disk load. If the workload exhibits a "locality of reference" behavior, where a relatively small set of data is accessed frequently and repeatedly, the read cache can improve performance. In read-intensive environments, where more than 70 percent of all requests are reads, the read cache should be large enough to accommodate the dataset that is most frequently accessed. For sequential reads from a LUN, data that is expected to be accessed by subsequent read requests is read (prefetched) into the cache before being requested. Therefore, for optimal performance, the read cache should be large enough to accommodate prefetched data for sequential reads from each LUN.
SPB_write_cache_size Indicates the current size of the write cache of Storage Processor B.   Write cache serves as a temporary buffer where data is stored temporarily before it is written to the disks. Cache writes are far faster than disk writes. Also, write-cached data is consolidated into larger I/Os when possible, and written to the disks more efficiently. (This reduces the expensive small writes in case of RAID 5 LUNs.) Also, in cases where data is modified frequently, the data is overwritten in the cache and written to the disks only once for several updates in the cache. This reduces disk load. Consequently, the write cache absorbs write data during heavy load periods and writes them to the disks, in an optimal fashion, during light load periods. However, if the amount of write data during an I/O burst exceeds the write cache size, the cache fills. Subsequent requests must wait for cached data to be flushed and for cache pages to become available for writing new data. It is hence imperative that you rightly size the write cache.
SPB_free_mem_size Indicates the amount of memory unused with storage processor B. MB  
SPB_sys_buf Indicates the size of the system buffer of storage processor B. MB  
SPB_phy_sys_mem Indicates the total physical memory of storage processor B. MB  
SP_read_cache Indicates the state of the read cache of the storage processor.   If the read cache of the storage processor (SP) is enabled, then this measure will report the value Enabled. If not, then, this measure will report the value Disabled.

The numeric values that correspond to each of the states discussed above are available in the table below:

Numeric Value State
1 Enabled
0 Disabled

Note:

By default, this measure reports the values Disabled or Enabled to indicate the status of the read cache. The graph of this measure however, represents the cache status using the numeric equivalents - 0 or 1.
SPB_phy_sys_mem Indicates the total physical memory of storage processor B. MB  
SP_read_cache Indicates the state of the read cache of the storage processor.   If the read cache of the storage processor (SP) is enabled, then this measure will report the value Enabled. If not, then, this measure will report the value Disabled.

The numeric values that correspond to each of the states discussed above are available in the table below:

Numeric Value State
1 Enabled
0 Disabled

Note:

By default, this measure reports the values Disabled or Enabled to indicate the status of the read cache. The graph of this measure however, represents the cache status using the numeric equivalents - 0 or 1.
SP_write_cache Indicates the current state of the write cache of the storage processor.   If the write cache of the storage processor (SP) is enabled, then this measure will report the value Enabled. If not, then, this measure will report the value Disabled.

The numeric values that correspond to each of the states discussed above are available in the table below:

Numeric Value State
1 Enabled
0 Disabled

Note:

By default, this measure reports the values Disabled or Enabled to indicate the status of the write cache. The graph of this measure however, represents the cache status using the numeric equivalents - 0 or 1.
Cache_page_size Indicates the number of pages currently in cache. Number To service I/O requests faster, to reduce disk overloads, and to eliminate disk abuse, the read/write caches should be sized with sufficient memory pages.

Ideally, a cache page can be of size 2, 4, 8, or 16 KB. As a general guideline, EMC suggests 8 KB. The ideal cache page size depends on the operating system and application.
Write_cache_mirrored Indicates the write cache mirrored status.   Each storage processor (SP) has a write cache in its memory, which mirrors the write cache on the other SP. Because these caches mirror each other, they are always either enabled or disabled, and always the same size. On powerup, a storage system automatically enables the write cache on each SP if the write cache size is non-zero.

Using this measure, you can determine whether the write cache of both SPs is currently enabled/disabled.

If the write cache is disabled, then this measure will report the value Enabled. If not, the measure will report the value Disabled.

The numeric values that correspond to each of the states discussed above are available in the table below:

Numeric Value State
1 Enabled
0 Disabled

Note:

By default, this measure reports the values Disabled or Enabled to indicate the status of the write cache. The graph of this measure however, represents the cache status using the numeric equivalents - 0 or 1.