HP ProLiant DL380G5-WSS 3.7.0 HP StorageWorks HP Scalable NAS File Serving Sof - Page 87

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 utility, 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 HP Scalable NAS File Serving Software administration guide 87