Storage System Performance

The Windows Vista storage test only assesses sequential read performance. This is sufficient to rank storage devices in a basic manner, but it does not account for random I/O performance, or for disk behavior in the face of mixed reads and writes. Thus, Microsoft added the following abilities in Windows 7 :

• Full random read and write assessments.
• Sequential write assessments
• Disk flush policy assessments (mixed reads and writes)

Several key usage scenarios benefit perceptibly from good storage performance, including:

• System Boot
• Resume from Suspend and Hibernate.
• Application launch
• Email application usage
• Desktop Search
• Paging scenarios on memory constrained systems

As with CPU performance, the challenge with scoring the storage system is identifying scenarios where notable scenario performance differences correspond to specific changes in storage system performance.  The clearest example Microsoft found is with the write flush policy – a poorly implemented policy has a notably adverse affect on User Interface (UI) responsiveness.

Therefore, the Windows-7 storage scoring plan is :

a) Retain the existing sequential read performance scale.

b) Cap the Disk score for storage systems with a poor write flush policy regardless of the system’s other performance parameters.

• The cap set in the Windows 7 preview build (6801) was 2.8.
• Based on analysis of lab runs over expanded set of hardware, there are two caps for Beta:
  • At 1.9, this corresponds to having either
    - IOs greater than 600 milliseconds, or
    - mean IO >= 22milliseconds and 95th percentile IO >= 40 milliseconds
  • At 2.9, this corresponds to either
    - IOs greater than 520 millseconds
    - Mean IO >= 11 milliseconds and 95th percentile IO >= 33 milliseconds

c) 5.0 to 5.9 represents disks with a good sequential read performance and a good write flush policy. Most mechanical drives are expected to show performance that is rated under 5.9.

d) 6.0 to 6.9 represents the expected performance for  storage devices that have very good random I/O performance.
- Note that most currently shipping devices in this class score in the 6.0 to 6.5 range.  As faster devices reach the market, they can achieve 6.6 and higher.

e) 7.0 to 7.3 maps to the best performing, currently shipping devices in terms of sequential and random I/O performance.
- We expect that over the 2010 and 2011 time frame, drives will dramatically increase in performance, so have left plenty of room in the 7.0 range for these devices.
- Devices in the 7.0 range can sustain high rates of both random and sequential I/O.

Notes

For Windows 7, random I/O performance is what distinguishes Good, Better and Best.

The assessments do not detect the platter geometries, RAID configuration, or storage technologies; the results are based on measured performance only.

During the Release Candidate period, Microsoft expects to update the metrics for the write flush policy tests based on results of further lab runs.

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