3.7.0 HP StorageWorks HP Scalable NAS File Serving Software administration guide - HP Scalable NAS 3.7 for Linux (AG513-96002, October 2009)

Disk partition alignment
Many disk arrays are sensitive to misaligned I/O operations and require I/O to be
aligned on block boundaries for performance reasons. For example, an array may
“prefer” to have I/O operations occur on natural block boundaries, such as 4-KB
blocks. If a partition starts at a non-block boundary, a single logical write can span
more physical blocks that it would on a partition starting on a block boundary,
resulting in additional I/O operations. The exact alignment characteristics vary by
manufacturer and model; consult your storage vendor for alignment recommendations.
This issue occurs because the partition table causes space to be reserved at the start
of the LUN, which can cause a misalignment with the array’s storage. If your storage
array is affected by this issue, the simplest way to avoid the situation is to create an
unused partition at the start of the LUN and then ensure that the second partition
starts on an aligned boundary. Utilities such as fdisk can be used to create the
partitions.
NOTE:
HP Scalable NAS supports unpartitioned disks. There are no alignment issues when
using unpartitioned disks.
Import SAN disks
SAN disks to be used for PSFS filesystems must be imported into the cluster. This step
gives the cluster control over access to the disks. Before importing disks, you should
be aware of the following:
• If servers from multiple clusters can access the SAN via a shared FC fabric, avoid
importing the same disk into more than one cluster. Filesystem corruption can
occur when different clusters attempt to share the same filesystem.
• If you want to change the partition table on a disk after it has been imported,
you will need to deport the disk, make the changes, and then import the disk
again.
• Disks containing an active membership partition cannot be imported. You will
need to use mprepair to inactivate the partition (see The mprepair util-
ity, page 365). After the partition is inactivated, you can import the disk into the
cluster.
• If you import a large number of disks sequentially, it can take several minutes to
complete the imports. The imports will be faster if you specify all of the disks in
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