From the Blogosphere
Maximize the Advantage of SSD Caching
How to Configure Your File System
Jan. 21, 2013 01:30 PM
File System Alignment for SSDs
There are many techniques and methods that can be used to tune an IT system to improve overall system performance. SSD caching is widely being used as a low cost, easy to implement method to quickly increase performance with little or no impact on existing operations. One thing that needs to be considered when choosing SSD caching is how to configure a file system to maximize the performance increase SSD caching provides.
Operating Systems and Block Size
In the past few years, the sector size of HDDs has increased from 512 bytes to 4k bytes. Relatively new operating systems (e.g. Windows Server 2008 R2 to present) have evolved to work with this not-so-new sector size to take advantage of higher density drives. Problems, however, can occur for older operating systems that were not designed to work with the larger block size devices. This becomes a critical issue when SSDs are introduced into the mix. SSDs are all designed to operate with a 4k block size (block and sector are used interchangeably). As a result, IT managers buying SSDs to improve system performance may not be getting the most out of their new, relatively expensive investment. Proper alignment of the file system may help to get better performance in this case.
Some Points to Consider Regarding Block Size and Alignment
Here are some things you should consider when using SSDs and modern HDDs in your system:
- Block size – always use 4k block size
- Block alignment – needs to be set to 4k. If the blocks are not 4K aligned, there is additional disk I/O overhead because 2x blocks need to be fetched for every access.
- Partition alignment – Ensure that the starting partition is aligned to 4k. If your system was upgraded from pre-Windows 2008 R2 OS, make sure you re-align the partitions to 4k.
- Memory allocation (Linux only - no control on Windows) [I could not figure out what to write about this]
- VMware environments – align all guest data disks on 4k boundaries
- Hyper-V – align all guest data disks on 4k boundaries
Best Practices Results
Optimizing your system according to the above recommendations can improve performance up to 50%. Most modern OS file systems use these methods by default so there is no need to do anything. XFS and Windows versions earlier than Windows 2008R2 do not do this alignment automatically.
Velobit HyperCache caching software operates based on 4k blocks. If your existing system is not set up to work this way, Velobit will still work with the different block size making Velobit an ideal way to get performance improvement for older, legacy systems. However, the performance increase provided by Velobit will be limited due to additional overhead associated with managing non-4k block sizes.
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