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Flash-Layer Performance Tuning
HP-AM456-9002A Rev 01
While these tests are running, use operating system tools to confirm that actual
I/O activity is similar to the levels tested using the
not similar to the baselines, then the operating system, file system, or database
may need to be tuned. Please contact HP Customer Support for assistance if
needed.
In a Memory Array system, the performance of the flash layer is a function of
several attributes of the flash-based memory arrays.
•
Type of VIMM (SLC or MLC): SLC is faster for writes
•
Number of VIMMs per Memory Array: 42/84 VIMMs are faster than 21
VIMMs
•
Formatted Capacity: 65% format is faster than 84%
•
Number of Memory Arrays: Like all storage media, more arrays provides
higher bandwidth.
Flash-based memory arrays are designed for 4kB block access or any multiple
of 4kB blocks. Smaller block sizes (e.g. 512 bytes) will significantly reduce
performance, particularly for writes. Therefore, it is import that you verify
whether the file system and operating system are 4kB aligned. For more
information see
Memory Array Flash 4kB Alignment
Random workloads with high IOPS are well supported by flash memory. Unlike
hard disk drives, sequential accesses are not significantly faster. For this reason,
it is typically better that higher layers are tuned for 4kB-16kB block sizes and
high IOPS.
Where an application needs very high bandwidth, multiple Memory Arrays are
recommended.
Flash Memory Arrays achieve maximum performance when large numbers of
flash devices are used simultaneously, which requires a large number of
simultaneous accesses by the application and file system. Typically, this is
enabled through asynchronous I/O and having many threads simultaneously
access the flash memory. Where this is not the case, this is known as single-
threaded access and severely limits performance.
Memory Array Flash 4kB Alignment
One major consideration for flash-based Memory Array system performance is
the 4kB address alignment on I/O requests.
The most common indication that a partition that is out of alignment is poor
performance; low read/write I/Os per second (IOPS). Partitions can easily be
out of 4kB alignment because most operating systems, when creating a file
VMA-series Memory Array Installation and Service Guide
Flash-Layer Performance Tuning
utility. If the I/O is
perf_test
on page 169.
169
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