![]() ![]() The myth that NTFS does not suffer from fragmentation is pure non-sense. ![]() Files that grow over time, for example databases and dynamic disks, are prone to fragment. Disk Fragmentation and Hyper-V Backupsĭisk fragmentation is also not a fantasy nor a FUD. This additional management requirement may be fine for one or two VMs, but if you have dozens on a busy server, the resources required to handle disk access all add up. In addition, even if you used SSD which has negligible seek times, due to its flash-memory-like internals, there is additional CPU and RAM required to index all blocks so that the system can track which file has which block and at which index. For example, the two blocks that are supposed to be next to each other on a fixed disk may in fact be at opposite ends on the physical disk. A simple two-block read which doesn’t require a disk head motion, may require a substantial disk head move when using dynamic disks. When dynamic disks are used, logically sequential blocks are not necessarily close to each other. However, seek times are a fundamental variable when blocks are written many thousands of times per second, as a on a busy server. In a fixed sized VHD, all blocks are located at a known location on disk which is linearly addressed hence, if you neglect seek time differences, each block is equally quick accessible. The reduction of performance due to fragmentation is based on plain physics and plain information science. Conversely, you could serve a substantial number of additional VMs if you used fixed disks throughout instead without checkpoints / snapshots. In many common usage scenarios, dynamic disks will cause the server to slow down considerably. ![]() Dynamic Disks and Disk Fragmentation and Reduced Performance Needs to be Dealt Withĭynamic disks cause disk fragmentation and require additional overhead to process disk read and write access. After that the VM is powered on again and continues where it left off however, the issue here is that network connections will break off and the VM won’t be accessible for that minute or two. Because the Hyper-V VSS Writer cannot handle live backups of dynamic volumes, the VM is paused for a minute or so until VSS is done with its prep work. Whether a backup is live (uninterrupted) or a Saved State backup, that’s controlled entirely by Hyper-V, not the backup application. See Live Hyper-V Backup using Hyper-V VSS Writer: How Backup Works. The result is then that the VM is pulled into a Saved State when a backup is requested. Naturally you could use dynamic disks inside virtual machines however, the Hyper-V VSS Writer still does not support them for live backup. ISSUES USING DRIVE SNAPSHOT WITH WINDOWS 10 RAID VOLUME SOFTWAREThe other kind of dynamic disk is the dynamic disk in Windows that offers software RAID and disk spanning features. Dynamically expanding disks (and hence checkpoints) shouldn’t be used on production systems as they often dramatically reduce performance by increasing overhead and fragmentation, see performance differences between fixed and dynamic VHDX. Hyper-V uses them internally also for checkpoints (a.k.a. Dynamically expanding disks are VHDX files that grow over time. Dynamic disks in Hyper-V may be a bad choice under certain circumstances, especially for Hyper-V backup and for general performance reasons.įirst of all we need to distinguish between dynamic disks and dynamically expanding disks. ![]()
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