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Microsoft Disk Alignment KB Disk performance may be slower than expected when you use multiple disks in Windows Server 2003, XP, and 2000: http://support.microsoft.com/kb/929491 -------------------------------------------------------------------------------- Disk terminology for the purpose of explaining sector alignment: Sectors, Tracks and Blocks * A sector is the smallest unit of storage space on disk and is typically 512 bytes. * A track is the circular path of sectors that sit around a single circumference of the disk. There are 63 sectors per track numbered 1-63 on each track. * A block is how you usually refer to sectors to make things easier for you. You start at the beginning of the disk and increment until the end of the disk. Blocks start from 0. Partitions always start at the first sector on a track, so for the first partition that means Track 2 Sector 1 (because the MBR is on Track 1), which equates to Block number 63 (blocks start from 0). Misalignment occurs because the storage vendors define tracks differently. On an EMC Symmetrix, for example, a track is considered to be 64 blocks and the cache is also based on this. A Symmetrix DMX RAID5 array uses a stripe size of 4 tracks, which totals 256 blocks. 64KB is the largest single write that Windows can make, so using the default partition location means that the first 64Kb write will be fine but the second will straddle 2 “stripes” causing both to be updated. If you align the partition to 128 blocks (or 64KB as each block is 512bytes) then you don’t cross a track boundary and therefore issue the minimum number of I/Os. There are 2 methods of aligning your partition and you’ll be pleased to know that it’s quite a simple process. Diskpar is a tool that’s been available for a while to enable you to align partitions but as of Windows 2003 SP1 the preferred method is Diskpart (note the extra ‘t’). The main difference between the two methods is that you specify the alignment value in blocks using Diskpar and in KB using Diskpart. -------------------------------------------------------------------------------- Tips: Modifying the “HBA Queue Depth” is a performance tuning tip for servers that are connected to SAN Storage. --------------------------------------------------------------------------------