[AccessD] This just in...

jwcolby jwcolby at colbyconsulting.com
Mon Jun 15 16:32:20 CDT 2009


I just found this:

It is highly recommended that all partitions are configured by using the DISKPAR (Windows 2000) or 
DISKPART (Windows 2003) commands. When using DISKPAR, adjust the alignment by 512 bytes, and when 
using DISKPART, the disk should be aligned to 64. The reason for this is due to the original master 
boot record design of WinTel based systems. The master boot record for all drives is 63 blocks (1 
block = 512 bytes).

The physical disks want to read and write data in 64 block chunks. Because the master boot record is 
only 63 blocks, this puts the first block of actual data in block location 64, where it should be in 
block location 65. That forces the disk to read 128 blocks for each 64 blocks read to the disk, 
thereby increasing the work needed to be done and decreasing performance.

It is so highly recommended that volumes be created with this 64 block offset that Microsoft is 
including this procedure as the standard when creating partitions starting in Microsoft Windows 2008 
Server. There are no published figures on what sort of performance improvement will be seen by 
creating your disks using this method. It's because any numbers would be relevant to only the system 
they were taken against, as all databases are different. Unfortunately, once a partition has been 
created without the alignment offset, there is no easy way to change the offset. The only method for 
doing that is to create a new volume and partition with the offset, take down the SQL Server and 
manually migrate the files to the new drive in an offline manor.

here:

http://searchsqlserver.techtarget.com/tip/0,289483,sid87_gci1262122_mem1,00.html

-- 
John W. Colby
www.ColbyConsulting.com



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