Overprovisioning is a common issue in data centers due to thin provisioning. While thin provisioning saves space, there is a performance hit and also an increase in the probability of running out of space in the storage group.
When blowing out space in a thin-provisioned virtual disk, many IT people turn to the free SDelete (Secure Delete) command-line utility. SDelete deletes existing files and erases any file data that exists in the unallocated portions of a disk (including files that you have already deleted or encrypted). With SDelete, you can also overwrite the contents of free space on your disk.
To use SDelete, you’ll need to write and test a script file. Besides the fact that you need to write a little code, SDelete has other issues that also make it non-optimal. SDelete completely fills a drive’s free space with a single file. For example, if a drive has 20GB of free space, the SDelete file will be written completely over the 20GB, wherever the free space exists. While this is occurring, you will need to minimize file activity, since SDelete runs at normal CPU and I/O priority, thereby consuming substantial resources on its own. If you have a drive that normally has a lot of activity,, such as a file server or SQL server, this can be a problem.
With PerfectDisk’s Zero Fill feature, available in PerfectDisk Server, PerfectDisk Exchange and PerfectDisk vSphere and PerfectDisk Hyper-V, SDelete’s shortcomings are overcome. PerfectDisk writes to the drive in small chunks of space, using Microsoft APIs (Application Programming Interfaces) and runs at low CPU and disk priorities. This strategy limits the disruption to the entire process of securely deleting files and space.
This gives storage and system administrators another option for zero-filling free space that offers additional benefits of lowering hypervisor overhead, improving disk latency and throughput, and reducing the size of virtual disks.
I’ll go into Zero Fill and thin-provisioned disks in more detail in a future post.