Pillar Axiom: How to Create SAN LUN Partition Alignment Offset in Windows

Asset ID:	1-71-1388348.1
Update Date:	2012-08-29
Keywords:

Solution Type Technical Instruction Sure

Solution 1388348.1 : Pillar Axiom: How to Create SAN LUN Partition Alignment Offset in Windows

Applies to:

Pillar Axiom 600 Storage System - Version Not Applicable to Not Applicable [Release N/A]
Information in this document applies to any platform.

Goal

This article describes the recommended method to set the correct alignment offset for Windows.

Fix

NOTE: When at all possible, it is highly recommended to use the diskpart command to create the primary partitions for the LUNs used for Windows storage. The advantages of providing an alignment that matches storage disk boundaries have been documented very thoroughly. (See http://support.microsoft.com/kb/929491 for example)

The partition alignment should be set to the size that is striped (or stripped, in the case of the Pillar Axiom array) to each drive. To complicate the discussion, the Axiom can destage data to drives in various sizes. Assuming Oracle ASM has not been selected for a performance profile, a single RAID controller will receive IO in 640kB chunks, and each drive in the RAID controller will receive data in 128kb strips for SATA, or 64kB for FC.

Internal testing via JetStress and IOmeter using typical IO load have shown relatively minimal difference in IOps performance between LUNs with the default alignment setting and LUNs with 64kB or 128kB alignment offsets. However, for SATA, the 128kB alignment does provide the lowest service times. For FC, 64kB or 128kB alignment provides the lowest service times. As IOps requirements increase, service times will obviously have a corresponding impact on overall IOps performance.

For simplicity, use 128kB alignment on all partitions to be used for standard Windows LUNs, whether the LUN resides on FC or SATA. Again, 64kB is correct for FC, but 128kB, being a multiple of 64kB, will work. To reduce confussion, 128kB will work on both SATA and FC.

For LUNs with an Oracle ASM performance profile, 1024kB should be used as the alignment offset.

Below is an example of setting a 128kB alignment offset for SATA Controllers.

C:\> diskpart



DISKPART> list disk



Disk ### Status Size Free Dyn Gpt



-------- ---------- ------- ------- --- ---



Disk 0 Online 100 GB 100 GB



Disk 1 Online 34 GB 4080 KB



Disk 2 Online 100 GB 100 GB



Disk 3 Online 100 GB 100 GB



Disk 4 Online 100 GB 100 GB







DISKPART> select disk 2







Disk 2 is now the selected disk.







DISKPART> create partition primary align=128







DiskPart succeeded in creating the specified partition.







DISKPART> list partition







Partition ### Type Size Offset



------------- ---------------- ------- -------



* Partition 1 Primary 100 GB 128 KB

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