HP VMA SAN Gateway for VMA-series Memory Arrays Release Notes - December 2012

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4KB might suffer a performance impact. Write performance is more seriously affected by non-4KB
alignment. For example, if a user application writes 512 bytes starting at the last 256 bytes of a 4K
page, the result on hardware would be two 4K read-modify-write updates.
In order to achieve optimal throughput and performance with the VMA-series Memory Arrays, care
should be given to tuning the intended application, data layout structures on the array, and the
connected host server.
Data layout structure alignment on VMA Array LUNs
The data layout structures created on the VMA LUNs by a logical volume manager and file system on
the host should be made so that they are 4KB aligned, meaning that partition sizes, LVM striping and
other data structures are 4KB aligned. Consider the following when creating data layout structures on
the VMA:
• Partition sizes are 4KB aligned
• Volume manager stripe sizes are multiple of 4KB
• File system blocks are 4KB aligned
ext2 filesystem is not supported
The ext2 filesystem on Linux distros has outstanding known data integrity issues. It is highly
recommended that you use an alternative filesystem such as ext3 or ext4 instead.
Tune application to issue I/Os which are multiple of 4KB
Most high level applications can be configured to issue certain I/O block sizes for increased
performance. Ensure that configured I/O block size and if appropriate the beginning block addresses
for I/Os are 4KB aligned.
Create multiple LUNs for parallelization of I/O for applications
Creating multiple LUNs on the connected VMA arrays might allow applications to launch multiple
threads for greater I/O parallelism and performance. It is currently recommended to configure no
more than 32 LUNs per connected VMA Array with this G5.5.1 release of the VMA SAN Gateway
software OE. Additionally for optimal I/O flow, it is recommended to not allow more than 16 total
lunpaths per LUN; total sum of all lunpaths to a LUN for all connecting servers.
LUN 0 of the VMA SAN Gateway
LUN 0 is considered a reserved device and various issues can occur if LUN 0 is not accessible by all
connected host servers. Thus, the VMA SAN Gateway will prompt for configured LUNs to begin with
LUN ID #1. If a specific operating system requires configuration of a LUN ID #0, this can be done by
explicitly entering ‘0’ for the LUN ID when creating a LUN. However, any configuration changes or
accessibility change to an explicitly created LUN ID #0 might cause disruption of service including
inability to discover and access LUNs and stored data to other connected server hosts.
Currently only 512B sectors are supported
While the VMA SAN Gateway will allow creation of LUNs with either a 512B or 4KB sector size,
only 512B sector size has been fully tested and supported with the gateway. LUNs using 4KB sectors
have not been fully validated and are not considered supported by HP at this time.