disk alignment best practices:
Why is disk Alignment needed ? When the disks of a VM are not aligned, any reads or writes to the physical disk (chunk) on which the VM resides, have to be done more than once, which can cause as much as 40% overhead in disk I/O. In the unaligned disks, if the cluster in the operating system is read or written to, then both the blocks of the file system and three of the chunks of physical storage need to be accessed in order to complete the read or write. In the aligned disks, if the cluster in the operating system is read or written to, then only one block and one chunk need to accessed in order to complete the read or write. The result of the problem causes the storage device to work harder than it needs to, which indirectly affects all servers using the storage device, even the aligned servers.
The aim of this sysadmin task is to align all servers and associated storage, to achieve optimum performance on all storage devices and the virtual environment. Currently there is a windows process and a Linux process currently being used to correct the problem.
a) Arrange a date and time with the application management teams and customer, when the application can be taken offline so the server can be powered down for the required length of time (several hours)
b) Record the server details and enquire if any amendment to the current storage layout are required
c) At the agreed date and time the server will be shut down and the Virtual Machines disks will be aligne
d) Upon completion of section 3, the server will be powered up and the customer will be requested to check if the application or service is still functioning correctly
e) The old disks will be kept for a period of 4 weeks, so if a roll back were required this could be performed
Checking SSD disk alignement on Windows:
To check the alignment of your SSD’s partition, it is quite simple.
In windows 7, run msinfo32 by typing it into the search box on your start menu and hitting enter.
click on: components => storage => disks
Look for your SSD and check the partition starting offset.
It needs to be divisible by 4096 (ie return a whole number when you divide by this) otherwise the alignment is not correct.
Using diskpart and wmic to check disk partition alignment:Basic Disk Partition Offsets: wmic.exe
Windows can be interrogated for disk-related information via Windows Management Instrumentation (WMI). A straightforward method for obtaining partition starting offsets of Windows basic disks is this Wmic.exe command.
Command Line Syntax:
wmic partition get BlockSize, StartingOffset, Name, Index The value for Index is the same as disk number in the Disk Management Microsoft Management Console (MMC) snap-in (Diskmgmt.msc); wmic volume can also be used to map disk indexes and drive letters.Dynamic Disk Partition Offsets: dmddiag.exe -v
The command-line utility Dmdiag.exe is used to determine the partition offsets of Windows dynamic volumes.
Important: Neither the output of the wmic command listed earlier nor any other tool designed only for basic disks reliably reports starting partition offsets of Windows dynamic disks.
The tool is available in the support tools folder of Windows Server 2003. In Windows Server 2008, the tool has been renamed diskdiag.exe.
To determine the starting partition offset of dynamic disks, execute the following command.
Command Line Syntax:
The output has several sections; the sections that are cogent to analyzing the starting partition offset of existing volumes are generated only if the -v switch is used. Those sections (and relevant columns) are:
Dynamic Disk Information (Rel Sec) LDM Volume Information (Rel Sectors)
Focus on these sections and columns. Subsequent sections of the output that report offsets can be misleading, and they are unlikely to be reliable for interpreting starting partition offsets of dynamic volumes. Note that Microsoft tools, including even dmdiag, may be unreliable for reporting starting partition offsets of dynamic volumes created by third-party vendors. For example, dmdiag does not report correct starting partition offsets of dynamic volumes created by Veritas Enterprise Administrator. In these cases, consult your vendor for the tools and techniques required for proper analysis.