Measure Reference Manual

• A read or write operation on an OSS regular file can be cached or noncached:
Noncached operations result in messages sent directly to DP2 and transfer only as much
information as the client specifies.
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◦ Cached operations utilize the file-system cache in the client’s CPU and can result in a
block read/write between the cache and DP2.
Block reads or writes occur on cache block boundaries (except for the last block of the
file) where a cache block is 4 KB. Block read operations try to read ahead to anticipate
any need for the information in the immediate future.
• The FILE entity counters for READS and WRITES count all logical file I/O operations, including
reads and writes using OSS cache. They do not include block operations to replenish cache.
Therefore, on a cache miss, six counters are incremented:
OSS-BLOCK-READSOSS-CACHE-READSREADS
OSS-BLOCK-READ-BYTESOSS-CACHE-READ-BYTESREAD-BYTES
• The FILE entity does not contain a counter for OSS block writes or block write bytes because
a cache write is not necessarily triggered by the owning file. These counters are added to the
DISKFILE entity.
• The OSS file system uses an internal algorithm to evaluate the effectiveness of cache file
operations. Under some circumstances, caching is turned off by the system for a file open, so
cache counters are not incremented.
Command Examples: OSS File Opens
These command usage examples illustrate the use of file identifiers in selecting Measure file reports.
OSS Opens of Disk Files
File opens of the same disk file share the same Guardian format file name and OSS file pathname.
To select file opens of the same disk file, use either its Guardian format file name or OSS file
pathname:
LIST FILE $VOL.SUBVOL.FILE:CRVSN
LIST FILE "/a/b/c"
The Guardian format name can be masked to select disk file opens with the same device name or
with the same device name and subvolume name:
LIST FILE $VOL.*.*
LIST FILE $VOL.SUBVOL.*
244 Entities and Counters