Disk alignment is very important in every Operating system environment. But when you are using a SAN and also using VMware you should take disk alignement in account.
![2011-04-29_135917](http://blog.zefat.nl/wp-content/uploads/2011/04/2011-04-29_135917.png)
Above you see that the Guest OS (for example Windows) is not aligned with the VMFS and the VMFS is not aligned with the Array Blocks. Meaning that 1 I/O can result into 3 I/O’s on the storage device.
Now the VMFS has been aligned, but the Guest OS is still not. Now an I/O can result into 2 I/O’s on the storage device. Beter, but performance can still be improved.
Now all File Systems are aligned. On I/O results into 1 I/O, because all beginning of the blocks are at the same position.
Only Windows Vista, Windows 2008 and Windows XP has a trick to avoid this:
![2011-04-29_140031](http://blog.zefat.nl/wp-content/uploads/2011/04/2011-04-29_140031.png)
Tags: 3Par, ESX, EVA, P2000 by Bert Zefat
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