3.6.0 Matrix Server Installation Guide (5697-7079, February 2008)

Chapter 3: Install PolyServe Matrix Server 17

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 Windows 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. The Windows Logical Disk Manager or utilities such as

diskpart can be used to create the partitions.

Partitions Containing Windows Filesystems

If you will be using an existing partition for a membership partition and

that partition currently contains a Windows filesystem, then that

filesystem must be destroyed. One method for doing this is to delete the

partition and then recreate it. This is best done before multiple servers

have access to the disk. If that is not possible, all other servers with access

to the disk must be forced to recognize the changes, either by rebooting

all those systems, or by manually disabling the ports on the FibreChannel

switch that connect those systems to the SAN. If using the second

method, disable the ports before making the partition table change, and

then reenable the ports afterwards.

Changes to the Disk Partition Table

We recommend that you do all necessary partitioning on disks that will

contain membership partitions before assigning the membership

partitions. It is best to do the partitioning before multiple servers have

access to the disk. If this is not possible, ensure that all servers having

access to the disk through the SAN detect the partition table changes

before continuing on with membership partition initialization.