HP-UX Encrypted Volume and File System Performance and Tuning

Figure 3 - EVFS threads

EVFS Memory Allocation

The HP-UX file system (JFS) allocates memory for user process applications using the buffer cache

feature. Applications that read and write data to an EVFS volume can use the buffer cache for read-

ahead and write-behind operations. Because the EVFS pseudo-driver exists below the file system

layer – and thus buffer cache – EVFS performance can benefit from correctly instrumented buffer

cache utilization. However, EVFS modules do not allocate memory from buffer cache – EVFS does

not directly use buffer cache at all.

Note: read-ahead and write-behind

Read-ahead and write-behind are file system features that can improve user

application performance by utilizing system buffer cache. For read-ahead,

the file system uses internal algorithms and configured variables to predict

what read data will be requested from storage media beyond the current

operation. The predicted data is then retrieved and stored in memory

(buffer cache) where access latency is significantly reduced, thereby

improving application performance. For write-behind, the file system uses

internal algorithms and configured variables to store application data that

is being written to storage media temporarily in memory (buffer cache)

while waiting for the file system to finish with the slower current task of

actually committing the data to disk. The application can continue to

process data as the file system writes data from buffer cache to storage,

again improving performance.

EVFS allocates memory for encryption and decryption operations from the HP-UX kernel arena

memory pool. Memory utilization from the arena pool increases as the EVFS load increases. On HP-

UX 11iv2 the total arena pool utilization can grow past the high-water mark, based upon the

requirements of the pseudo-driver. However, maximum usage for the test environment for these

benchmarks was 500MB.

The graphic below displays the memory consumption of HP-UX 11iv2 at system startup with 64GB

available memory. System memory utilizes 3.6GB of memory at startup, and buffer cache is