Measuring Windows ReadyBoost Performance

If it is affordable and practical, the first step in tuning a typical system should be adding RAM.  After that, ReadyBoost can relieve pressure on the hard drive.  ReadyBoost particularly benefits systems with limited RAM and slow hard drives.  Any system with over-worked hard drives (queuing, swapping) will likely benefit, particularly older systems with limited RAM.  Laptops with hard drives typically benefit, and a low-profile CF or SD card may be a more practical option than a bulky USB drive.

While the smallest cache size is 256MB, larger is better.  Sizes larger than RAM can be beneficial, so 1:1 for RAM sizing is not a useful rule of thumb for sizing.

ReadyBoost requires 2.5MB/sec for reads and 1.75MB/sec for writes.  Typical USB setup is exFAT with 4k sizing.

ReadyBoost was introduced in Windows Vista for one flash drive.  The flash drive capacity was increased in Windows 7.  Windows 8.1 allows for multiple ReadyBoost drives.

After ReadyBoost is running, it can be monitored with Perfomance Monitor.  Press Windows+X, choose Run, type perfmon


Press the red X to stop monitoring.


Press the green + to configure.


Click ReadyBoost Cache



Press OK and monitoring will begin.


Uncheck some of the monitors, to reduce the visualization.  You probably don't want both monitors for reads & bytes.

The histogram visualization may also be useful.

Cache reads indicate ReadyBoost is relieving reads from the disk drive, which should make the system feel more snappy.  For a large USB drive, it will take days of system usage to fill the cache with typically-used data.  Wait a few days before deciding to keep or remove the ReadyBoost cache.

Command Line Formatting For ReadyBoost

After purchasing a fast 120GB USB drive, I found it was formatted as FAT.  I attempted to format it as exFAT via the Windows Explorer in Windows 8.1, and Windows Explorer repeatedly crashed.  I was able to format the USB drive from a command prompt.

Open a command prompt by pressing the search icon in the charms bar and type "cmd".  Alternatively press Windows key + x, choose Run, type "cmd".

In the command prompt, type:
M:\>format /FS:exfat /A:4096 L:
Insert new disk for drive L:
and press ENTER when ready...
The type of the file system is FAT32.
The new file system is EXFAT.
Verifying 119.2 GB
4 percent completed.

4096 is the allocation size. This is not the size of the entire USB drive.

After a long-running verify process (/Q may be useful), the command prompt will look like:
M:\>format /FS:exfat /A:4096 L:
Insert new disk for drive L:
and press ENTER when ready...
The type of the file system is FAT32.
The new file system is EXFAT.
Verifying 119.2 GB
Volume label (11 characters, ENTER for none)?
Initializing the File Allocation Table (FAT)...
Creating file system structures.
Format complete.
     119.1 GB total disk space.
     119.1 GB are available.

        4,096 bytes in each allocation unit.
   31,217,972 allocation units available on disk.

           32 bits in each FAT entry.

Volume Serial Number is 38E3-EE45

A subsequent quick reformat was indeed quick.
Through driver properties, ReadyBoost was set to use the entire device.
L:\>dir
 Volume in drive L is New Volume
 Volume Serial Number is 2EBF-E89F

 Directory of L:\

2015.02.18  12:31 AM    34,359,738,368 ReadyBoost.sfcache
               1 File(s) 34,359,738,368 bytes
               0 Dir(s)  93,608,476,672 bytes free

From the help of the format command, this is the description about allocation size:

  /A:size         Overrides the default allocation unit size. Default settings

                  are strongly recommended for general use.

                  ReFS supports 4096, 64K.

                  NTFS supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K,

                  128K, 256K, 512K, 1M, 2M.

                  FAT supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K,

                  (128K, 256K for sector size > 512 bytes).

                  FAT32 supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K,

                  (128K, 256K for sector size > 512 bytes).

                  exFAT supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K,

                  128K, 256K, 512K, 1M, 2M, 4M, 8M, 16M, 32M.