VMware拟架构解决方案.ppt

This diagram shows what happens when you migrate storage in vSphere 4. First, upon initiating a migration, vSphere copies all virtual machine files except the disks from the old virtual machine directory to a new directory on the destination datastore. Second, vSphere enables Changed Block Tracking on the virtual machine’s disk. Changed block tracking tracks changes to the disk so that vSphere knows which regions of the disk include data. vSphere stores this data in a bitmap that can reside either in memory or as a file. For Storage VMotion, vSphere usually keep the change bitmap in memory, but for simplicity we’ve shown it next to the disk on the source datastore. Third, vSphere “pre-copies” the virtual machine’s disk and swap file from the disk on the source to the disk on the destination. During this time, the virtual machine is running and may be writing to its disk. Therefore, some regions of the disk change and must be resent. This is where changed block tracking comes in. vSphere first copies the contents of the entire disk to the destination; this is the first pre-copy iteration. It then queries the changed block tracking module to determine what regions of the disk were written to during the first iteration. vSphere performs a second iteration of pre-copy, only copying those regions that were changed during the first iteration. Typically the number of changed regions is significantly smaller than the total size of the disk, so the second iteration takes significantly less time. vSphere continues pre-copying until the amount of modified data is small enough to be copied very quickly. Fourth, ESX invokes fast suspend/resume on the virtual machine. Fast suspend/resume does exactly what its name implies: the virtual machine is quickly suspended and resumed, with the new virtual machine process using the destination virtual machine home and disks. Before ESX allows the new virtual machine to start running again, the final changed regions of the source disk