Windows SAN boot disk alignment

Question

We are in the process of setting up for IBM Blade Servers for boot from SAN on our cx700 to a Windows OS. We have in the past used the following command for any secondary luns (outside of the c drive) to get the disk alignment configured properly for that partition. For example a new LUN to a host (that has local boot disk) that is going to get a new E drive.

diskpart> create partition primary align=64

Once we run this command we do the rest of the setup and formatting and needed.

How do we accomplish this on a LUN where the host is booting from the SAN? The windows server blue screen setup does not allow use to do this. ie the c drive. The command above requires a OS to already be running.

In short how do we properly align a LUN that has no windows OS on it yet and that is going to be booting a Windows OS? We have read emc104675 over and over and it says nothing about SAN boot drives.
Thanks
Cory B.

dynamox · Answer

i have never done it myself ..but was wondering if you could boot from Windows PE and try it. You might need to have your Qlogic/Emulex floppy ready to press F6 to provide the driver so it can see the LUN.

AranH1 · Answer

Vista has a full Windows PE environment on it that your could boot into and use diskpart to create the parition, assign a drive letter, and format it.

I am curious though how important the partition alignment is for the OS drive. The recommendation from EMC for a partition aligned with the RAID stripe is meant to minimize disk crossing when writing data to a LUN to improve LUN performance right? How big of an issue is this for the OS LUN? After the OS and all applications are installed the OS drive is not an i/o hot spot and is not engaged in a lot of writes compared to data LUNs. So is this really a concern for the OS LUN?

What do you all think?

Aran

Kiran3 · Answer

if the swap file is on the bootdisk then alignment can be issue.can someone tell if setting alignment is required on host if its setup on array too?

AranH1 · Answer

Cory,If pagefile performance is a concern, why not create a second LUN for the pagefile after the OS is installed and create it with the proper alignment, then move the pagefile to it?

Bowling1 · Answer

We encountered the same 'issues' with aligning the boot partition and use PE to align our boot disk. We also standardized placing the pagefile on the boot partition as it was easier to get dump files during the dreaded 'blue screen of death'...

coryb1 · Answer

Thanks for the replies. I was guessing I would have to use a Windows PE boot and do that process. I am going to assume that I/O would be a issue as well like stated in one of the replies, because of the swap file. It is also safe to assume though that if you are doing heavy hits to the swap file you probably have a physical memory issue that should be addressed, which falls back to the one reply of OS drive shouldn't be doing heavy hitting to the c drive during normal operations, except during boot.....

I am taking the route of not doing the alignment. Thanks everyone for your replies. I think I got what I needed.

AranH1 · Answer

Bowling,Thanks for the reply, I was hoping to hear from someone who has done this. What was the driving factor for you to implement boot from SAN? Do you have any real world pros and cons about your experience with it?Aran

StevenXiao · Answer

Hi,I am just thinking why not you assign the alignment when you binding the LUN, when you firstly bind the LUN, you can assign the number you want, it should be 63 for NTFS volume if I wasn't wrong.Regards,

StevenXiao · Answer

Why not assign the alignment when you firstly bind the LUN, you can input the number you want, then the LUN will start at the alignment you assigned, for NTFS, the number should be 63. Because it was set up at the LUN binding, so it doesn't matter you use it for boot or non-boot LUN.
Regards,

CLARiiON

Windows SAN boot disk alignment

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