Storage I/O Misalignment – The Silent Performance Killer


February 8, 2013

Much like the medical industry refers to  high blood pressure or diabetes as a “silent killer,” storage I/O misalignment can slowly degrade the health and performance of your storage array over time.  I/O misalignment can degrade your applications & databases performance by as much as 30% or more, depending on how heavily those applications and databases are accessed.



The issue is that many IT professionals install the operating systems which these Apps & DBs reside on, without knowledge of the block boundary offset that the OS begins to lay the data down on. The reason this is a “silent killer” is that over time, the more you continue to install misaligned OSs, DBs & Apps, the slower all of your Apps & DBs will respond due to overall storage array I/O depravation, higher I/O latencies and higher CPU levels.


Where I/O Storage Misalignment Is Most Common


Misalignment is very common in virtualized environments because while the hypervisor (like VMWare) may natively be aligned, the Virtual Machine guests may not be. Newer operating systems like Windows Vista, 2008 Server and later will natively align to the correct bit boundary so misalignment should not be an issue. However, certain flavors of Linux, Unix & Windows 2003 Server and earlier will more than likely have misalignment issues if this issue wasn’t addressed when the OS was installed.

The reason misalignment is so common these days is as the disk industry evolved, the manufactures moved from the 512 Byte disk sector boundary to the 4KB boundary. The industry shift was made so that the offering of the disks sizes could be increased to the sizes we are using today.  For details on this evolution, refer to “Analysis: The Impact of Shifting from 512Bye to 4 KB Sectors” published on Tom’s Hardware.


How To Detect Storage I/O Misalignment


Without the proper tools to detect I/O misalignment, this issue can go undetected for years. If you would like to know if your storage array environment is operating optimally, or are concerned that you are experiencing storage array performance issues, please contact Mindsight’s Solutions Architect team to explore your options about having a Storage System Assessment performed by Mindsight’s Data Center Professional Services team.

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For Further Reading

Case Study: Eliminating the Storage Bottleneck with a Flash Array

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