Windows 7 will treat SSDs different to HDDs

Solid State Drives (SSD) have several significant advantages over traditional hard disks such as faster read performance when reading data from multiple areas of the disk, less generated heat and lower consumption.  However, the first generation of SSDs failed to live up to their hype for several reasons, as operating systems are not optimised for SSDs, many of the first SSDs were of poor quality and SSDs take up to 100 times longer to write data than reading it back according to SanDisk.

Windows 7 will improve upon Vista and XP in 4 ways when it comes to SSDs.  When Windows 7 detects an SSD, it will disable disk defragmentation for that disk, as defragmenting an SSD will cause wear and tear on the SSD without actually improving performance, unlike traditional hard disks.  Next, Windows 7 will feature a "trim" feature to reduce the amount of garbage data being written and deleted.  During a Windows 7 installation on a blank SSD, it will partition the SSD more efficiently to reduce unnecessary read/write operations.  The final feature will be Microsoft’s planned certification program for SSDs where SSDs must properly identify themselves to Windows, prioritise reads over slower writes and comply with the SATA drive interface to receive a certification logo. 

Even with these improvements, software developers will also need to change their software to make more efficient use of SSDs as the OS is not the only software that writes data to SSDs.  Unfortunately, many software developers have no plans to optimise their software for better SSD performance.  Even Microsoft could make more drastic changes to Windows to reduce the number of writes to SSD, such as improving write caching in RAM to reduce the number of physical writes to disk.  Intel is currently working on its Non-Volatile Memory Host Controller Interface (NVMHCI), which will eventually replace the SATA interface that was originally developed for hard disks, which should improve performance with an OS that takes advantage of the controller. 

Our senior reviewer Wendy has posted her experience with using two OCZ Core V2 SSDs in a RAID setup with 128MB cache, which clearly shows just how well SSDs can perform when coupled with a large cache for write operations.  While it’s no surprise here that a large cache for write-back operations will drastically improve performance, a write cache does have a drawback in that it needs safe guards to ensure all cached written data is written to disk before its power source is cut off.  Generally this happens with a proper shut down, but not if the PC experienecs an unexpected power outage or is forcefully powered off. 

For example, if a 128MB cache is maxed out with data waiting to be written to disk and the PC’s power source is cut off, this will cause up to 128MB of data loss, which the OS would have considered as already written to disk during its write operations.  This could result in a serious issue if critical write operations such as updates to the file allocation table were still in the cache, but not yet written to disk.  As a result caching write operations, whether in RAM, on the controller cache or on the SSD cache is not an ideal solution, especially on laptops where aging batteries often cut the power unexpectedly.  A battery-backed cache or adding a reliable UPS with shutdown software would solve this issue, but both add a significant cost.