Alignment of NTFS partitions on VMDK files

[polysulfide]

The whole concept of aligning partitions is fairly new to me but it does make a lot of sense. I've never needed (or at least known that I needed) to align paritions on NTFS volumes.

I recently ran the SQL 2005 BPA on a VM in an effort to maximize my success virtualizing an SQL server. The BPA told me that my partitions were mis-aligned. After some research it turns out that even NTFS volumes on standard raid hardware benefit from proper alignment.

I created a clone of my server to test aligned and non-aligned partitions. I'm currently running IOMeter for some quick initial tests but check this out......

I moved all my data from D to E (identical VMDK files on the same LUN), this took 5 minutes. I then re-partitioned D on a 64k offset. Moving the data back took 45 seconds.

It seems like this is a SIGNIFICANT performance issue. I'm going to get creative to put the C: drive of my templates on the 64k offset but I'm curious why I haven't seen any information regarding this. I've been tuning servers for a LONG time and I've never run into this information before.

If it was useful, give me credit

Jason White - VCP

[dominic7]

See also: http://www.vmware.com/pdf/esx3_partition_align.pdf

I haven't done any timings with disk alignment, but your numbers seem to be outside the bounds of what VMware presents in this paper. I would be interested to see more data.

[williamarrata]

This is a good document pertaining to VMFS Alignment and why.

Track alignment for both physical machines and VMware VMFS partitions yields I/O performance improvements such as reduced latency and increased throughput. Creating VMware VMFS partitions using the VI Client results in a 64KB-aligned partition table and provides the foundation for a best practices storage layout.

Hope that helped.

[polysulfide]

I understand what both of you are saying and I understand how the alignment works. But I'm not talking about aligning VMFS volumes to physical RAID disk. I'm talking about aligning OS volumes to vmdk files presented as Virtual LSI RAID disks. Such as:

DISKPART> Select Disk 2

DISKPART> create partition primary align=64

I'm not an expert at IOmeter but I'm seeing up to 9x improvement on some statistics and I can casually observe a 2x improvement in disk-disk file copy.

This suggests that there is a possible alignment issue using default partion alignments in your OS much like on a physical server.

I just thought I would share as much as ask why I haven't seen any info on this previously.

[JDLangdon]

I understand what both of you are saying and I understand how the alignment works. But I'm not talking about aligning VMFS volumes to physical RAID disk. I'm talking about aligning OS volumes to vmdk files presented as Virtual LSI RAID disks. Such as:

DISKPART> Select Disk 2

DISKPART> create partition primary align=64

How did you determine that your ntfs partitions were not aligned and how did you align them? Was it just those two diskpart commands?

________________________________

Jason D. Langdon

This space is for rent.

[williamarrata · Accepted solution]

Starting on the bottom of page 3 of that document, it goes into detail about the windows partitioning.

Hope that helped.

[polysulfide]

You're right, perfect, I'msorry I didn't read the whole document.

If it was useful, give me credit

Jason White - VCP

[polysulfide]

The SQL 2005 Best Practice Analyzer warned me that my disks weren't aligned properly. That's how I got started on all this.

Now I'm going to create new templates with properly aligned C: drives.

[proden20]

I've taken my grand old time getting around to doing this. I receive "The arguments you specified for this command are not valid." Guest OS is WinXP SP2. The PDF says to "make sure there is no data on the disk." If the only disk you have is the OS volume, how is that possible? Am I missing something?

Thanks!

Dennis.