[PDF] Parallels Server 5 Bare Metal

Advanced Tasks
In this example, any cluster (the smallest unit of data) in the guest OS file system is aligned with the
boundaries of an NFS block, and reading from or writing to a cluster requires only access to one
NFS block. For example, reading from Cluster 1 causes only a read from Block 1.
At the same time, virtual machines running non-modern systems (for example, Windows Server
2003 or Red Hat Enterprise Linux 5) do usually have misaligned partitions, which is shown in the
figure below:
In this example, clusters of the guest OS file system do not match the boundaries of NFS blocks,
and reading from or writing to a cluster requires access to several NFS blocks. For example,
reading from Cluster 1 causes two reads: from Block 1 and from Block 2. This results in a slower
read time as compared to properly aligned partitions and leads to performance degradation.
Aligning partitions
Basically, to align disks and partitions in virtual machines, you need to set an offset so that clusters
in the guest OS file system match the volume block size on your NFS storage. Usually, the block
size of most network storages is 512 bytes or a multiple of 512 bytes. As an example, the following
sections describe the procedure of aligning disks and partitions for Linux and Windows virtual
machines assuming that the size of your NFS blocks is 512 bytes.
When deciding on aligning disks and partitions, take into account that this process destroys all data
on these disks and partitions. So if you want to have a correctly aligned system partition, you need
to align your disks and partitions before creating a virtual machine and installing a guest operating
system in it. If you do not want an aligned system partition, you can first create a virtual machine
and install a guest OS in it, and then align your data disks from inside the virtual machine.
The sections below demonstrate how to align disks and partitions before you start installing a guest
OS. You can, however, use a similar procedure to align data disks and partitions from inside your
virtual machines.
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