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Alignment Overview

Alignment Overview. 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

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Alignment Overview

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  1. Alignment Overview NetAppPublic

  2. 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 NetApp Public

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

  4. Misaligned IO is a common problem NetApp Public

  5. Available Alignment Toolsmbralign • 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. NetApp Public

  6. NetAppPublic

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