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what is storage alignment, what is the benefits of it.

Jason Yu
Jason Yu asked
I have a question from my coworker, he is the oracle DBA.

He asks me "Did the OS disk partition aligned in the VMs built for this purpose as well as in the template, RHEL5U8_ORAC11gRAC_temp?


what is the alignment ? what is the benefits of doing it.

Please advise, thank you.
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as far as I am aware, this has not been an issue sense ESX 4.x.  You an check with your storage vendor.  Basically it is defining a starting block for the partition to increase performance.  In v5 it is 1MB for all filesystems created, but old upgraded vmfs partitions could be 64KB.  You would have to remove the partition and recreate it.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017
Performance of the VM disk I/O with the storage system.

Misaligned can cause degradation of VM db.

What is the storage system e.g. SAN

Check with SAN vendor NetApp have specific tools to use and fix.


We have netapp sans. Ef 550 and 8040 cluster. How can I make the storage aligned with os  ?
noxchoIT Product Manager
Top Expert 2009

You align the OS partitions to the storage. Not the storage to OS.
Distinguished Expert 2019
https://kb.netapp.com/support/index?page=content&id=1014111 is relevant to the 8040 which is classic NetApp.

As far as the all flash SANtricity EF550 is concerned it looks like it's impossible to misalign the storage as it uses 4K blocks natively.

www.vmware.com/pdf/esx3_partition_align.pdf has drawings to show what misalignment means - you could have to read 3 disk chunks to fetch a single data block , see the "Background" section of that document.

As already mentioned, recent versions of VMware, Windows and Linux automatically create an aligned filesystem so you don't have to worry about it any more.

Run fdisk -lu (or tell him to do it himself) to put his mind at rest.
VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017
I would conduct your own tests in my experience DBA seem to get very excited about misaligned VMs and disks ....

I would test aligned versus unaligned in your environment for your database application and then see if you notice a difference.


very good replies, thank you all, experts!