Disk Write Performance

- How Does Macrium Reflect Determine the Best Method?

- Which Disk Write Method is Being Used?

Overview

Creating a disk image involves moving large amounts of data as quickly as possible from the source partition to an image file on the destination disk. To ensure that images are created on local drives as fast as possible, it's essential to use the best method when writing image file data.

Understanding Disk Write Methods

There are two distinct ways of writing data to the destination disk:

Direct Disk I/O - This bypasses the file system cache and writes directly to the disk. For normal write operations in Windows, this will be a slower operation as the file system cache does a great job of asynchronously flushing its cache as well as using the cache to satisfy reading of the same data. However, for image files, where the data is sequentially written and there are no reads on the file system, using 'Direct Disk I/O' can offer significant performance gains.

This may not be the case for all disk and file systems, especially if the target file system is fragmented or nearly full.

File System Cache - This is the standard method of writing a file to a Windows file system. It uses the file system cache to buffer image file data and will flush the cache to disk when either the cache is full or the image file seeks to a different part of the disk to continue writing. This is usually faster for disks that have other processes reading or writing to the same disk, or if the file system is fragmented.

Other factors that may affect the speed of a disk write method include software RAID (dynamic) disks and hardware/firmware RAID setups.

How Does Macrium Reflect Determine the Best Method?

Macrium Reflect will automatically determine the best method for writing to a target drive the first time the drive is used as a backup destination:

To do this, Macrium Reflect will simulate creating two 1 GB files on the target drive. This will generally only take a few seconds to complete and will only happen the first time the drive is used as a destination. The fastest of the two methods is saved for the drive and will be used for subsequent backup creation to that destination drive.

Which Disk Write Method is Being Used?

The result of the disk write speed check can be viewed and overwritten in the 'Disk Write Performance...' dialog found under the 'Backup' dropdown menu:

In the window that opens, the drive will be displayed with the results of the disk write speed check shown under 'File System Cache' and 'Direct Disk I/O'. The 'Method' column shows which method is being used; this will be the faster of the two methods, unless the method has been changed from the default.

The following options are available in this window:

Option	Description
Add	This will add a new drive and perform the disk write speed test. Subsequent backups to this drive will not require the test to be performed before the backup starts.
Edit	This enables the default disk write method to be changed for the selected drive:
Delete	Remove the drive from the list of tested drives. If subsequent backups are created to this drive, the drive will be automatically retested and added to the list again.
Test	Perform the disk write speed check again as described here. The results in the 'Disk Write Performance' window will be updated.
Close	Close the dialog.
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