Alignment Overview 1 NetApp Public

What is Misalignment?  Misalignment is a condition where a single client IO operation results in multiple shared storage device IO operations because the IO boundaries of the client are not aligned with the IO boundaries in the shared storage device  The impact of misalignment is reduced performance on the shared storage device  The most frequent cause of misaligned IO is the default disk layout of many common client operating systems.  Misalignment reduces performance of most shared storage devices 2 NetApp Public

3 Client OS Misalignment Physical Disk Shared Storage Logical Disk Device manages data in 512 byte sectors Device manages data in multiples of 4K bytes Partition OffsetFilesystem Block Filesystem blocks are sector-aligned Default installs work on physical disks because file system blocks align on their sector boundaries Disk layout produced by default installs of common guest OS I/O to FS block Affects 1 sector range Default installs cause problems on logical disks because file system blocks don’t align with logical blocks Partition OffsetFilesystem Block Filesystem blocks are not block-aligned Disk layout produced by default installs of common guest OSs I/O to FS block Affects 2 logical blocks Filesystem Block Correct guest OS disk layout – requires non-default install for common guest OSs Partition OffsetFilesystem Block Non-default install provides optimum performance I/O to FS block Affects 1 logical block Non-default partition offset Filesystem Block

Misaligned IO is a common problem 4 NetApp Public VendorDevice/ApplicationPerformance Result/Best Practice EMCCelerraSql Server 40% improvement after alignment EMCClariionFilesystem misalignment affects performance EMCSymmetrix20-30% improvement after Win2K/2K3 alignment HPEVASet sector alingment to 64 using DiskPar IBMSVCAlignment of 64 will provide best performance IBMDS8000Align VMFS and clients for best performance MicrosoftWin2K/Win2K3Align partition start on stripe boundary MicrosoftExchangeAlign starting offset with storage track boundary NetAppAll storage controllersAlign filesystem start with block boundaries OracleSun Storage 7000Align IO to the block size of the LUN OracleOracle DatabasesSet block size relative to stripe depth VMwareVMFSAlign VMFS partitions on 64K boundaries

Available Alignment Tools mbralign  Utility used to identify and correct misalignment of VMDK partitions –Uses ESX console for VMFS and NFS based datastores –Can also be used on unix/linux hosts for NFS based datastores  Available as part of two “no-charge” software packages –ESX Host Utilities –Virtual Storage Console for VMware vSphere (VSC)  Limitations –Off-Line Alignment Only  VM must be shutdown to perform the realignment –Only works on ESX. –Full data copy required  Can take minutes to hours to complete depending on size of virtual disk  Latest version has the ability to offload data copying to the storage controller when aligning VMDKs on NFS datastores. 5 NetApp Public

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