Hard Disks are pretty bad regarding random data reading and writing. To compensate for these operations, a small amount of high-speed memory is installed with the hard drive as a cache or buffer. Its main purpose is to store recently or frequently accessed data and improve read/write and overall performance.
The controller on the hard disk will decide which data should be stored in the cache. For example, if you are running Google Chrome on your system, it will automatically store important files like cookies in the cache to improve application performance.
Hard disk cache is generally made up of the DRAM cache due to its high speed and efficiency. It is also used in DRAM SSDs. In hard drives, the main purpose of this cache is to give an artificial performance boost.
Without a cache, a hard drive can give many drawbacks to the overall system performance. So, it is an important factor when choosing a new hard drive. Let’s discuss everything in detail.
Purpose of Hard Drive Cache
The main role of hard drive cache is during the read operations. When the host asks for any data, the hard drive controller first checks in the cache if that data is present there. If data is present in the cache, it will send it back from the cache at a faster pace. If it isn’t available in the cache, it would read from the platters at a slower speed.
Cache Population
If the data requested by the host isn’t available in the cache, it is called a cache miss. The hard drive has to access the data from the platter but it won’t send the data to the system but also save a copy in the cache. In addition to this data, some related data is also stored in the cache.
Not all the data can be stored in the cache because of its limited size. Hard drives often use the LRU algorithm to manage this limited space and choose the best type of data to store in the cache. LRU keeps replacing the old data with new ones as the system requests new data.
For cache population, the controller also does read-ahead caching which involves reading and storing more data than requested for further improvements. Also, there are adaptive algorithms that learn from usage patterns and prioritize frequent data over other data.
The best example of a cache population is the boot-up process. Because the booting process demands a similar amount of data, the hard drive caches these files.
Speed up write operations
Write caching is another major purpose of the hard drive cache. In this process, the hard drive cache acts as the buffer to store the incoming write data temporarily. This improves the perceptive write speed and when the drive is free, the stored data is written on the platter for permanent storage.
The write cache allows the CPU to be free from the write operation almost instantly because of the write cache. Then it can perform its work.
Data inside the cache is organized before it is written to the disk. This allows the data to be written sequentially instead of writing it randomly as it comes from the host. Because of this, the data can be stored in continuous blocks thus increasing the storage speed.
There are two types of write caching in hard drives i.e. Write-Through and Write-Back caching. In Write-Through, the data is written both on disk and cache. It doesn’t provide much benefits in performance. In the Write-Back caching, the data is written later in the disk thus the write speed is improved.
Reduced Mechanical Wear and Tear
Another purpose of hard drive cache is to minimize the wear and tear on the hard drive platters. This is done by efficiently using the mechanical platters using sequential data writing as we discussed above.
Real-World Benefits of cache in hard drives
1. Improved Performance
The first real-world benefit of hard drive cache is improved performance both in random and sequential read/write operations. Whether you are running software or moving files to the drive, you will experience faster speed as compared to the drives without a cache.
2. Improved energy efficiency
With the optimized read/write operations, the unnecessary platter and heat movements and minimized. Caching also allows the hard drives to enter idle modes for much longer durations hence reducing the overall power consumption. It helps more in the battery-power systems such as laptops.
3. Enhanced Multitasking capabilities
With the help of caching, the hard drive can serve multiple data requests at a time. This is beneficial when you are using multiple software at a time. Although, you can’t expect the same multitasking capabilities as SSDs, a hard drive with a cache is great for low-end systems allowing them for better performance.
4. Better performance in high-load situations
In server and datacenter environments, caching can be pretty beneficial to divide the load evenly. It is great to handle the burst inputs of data and then manage the slower write operations for later. A cache can help avoid slowdowns and crashes because of hard drive bottlenecks.
5. Reduced Latency
With the help of a write cache, the perceived time taken for writing and reading data is reduced. This results in lowered latency. For systems that require quick data storage like databases and real-time logging systems, this can be pretty beneficial.
There are many more benefits of having a cache with your hard drive such as support for larger data sets and backup efficiency. Some caching systems also include support for error correction which can help in data integrity and storage reliability.
What are the drawbacks of hard drives without caching?
Some cheap drives come without any sort of caching mechanism. These drives offer some serious disadvantages over the drives with caching.
Because there is no buffering, the data is written directly to the platter. This makes the process slower and the CPU has to keep waiting until the data is completely written. The latency is increased because the data access time is increased.
Without the cache, the incoming data can’t be grouped as sequential or partially-sequential data which could be stored at a faster rate. The data is fragmented and this results in performance degradation.
The multitasking performance decreases and power efficiency is decreased. The level of wear and tear increases which results in a shorter lifespan of the drive.
However, there are applications for these drives in legacy systems that are more cost-sensitive. The hard drives without caching are considered extremely low-cost storage which is generally utilized where performance and data integrity aren’t very important.
64MB vs 256MB vs 512MB of Hard Drive cache
There are many sizes of cache for hard drives. Three main sizes are 64MB, 256MB, and 512 MB.
64MB generally comes with low storage capacity drives. This is good for basic caching and suitable for general tasks such as text editing, web browsing, and media consumption. Generally found in budget drives, these drives are suitable for low-end systems and put a storage bottleneck on high-performance computers.
256MB offers a good improvement in performance including better multitasking and sequential write operations. These are mid-range drives suitable for basic tasks including some kind of gaming and multimedia. However, you can’t expect great results on high-end systems.
512MB is more of a high-end cache size that comes with expensive drives. These drives are focused on high-end systems, significantly improving multitasking capabilities and read/write performance. They are perfect for data-intensive workloads. However, their prices could be higher.
In simple words, the higher the cache size in hard drives, the better it will be for multitasking, gaming, read/write performance, application usage, etc.
How do you assign an external cache to a hard drive?
There are two main methods to use an external cache with your hard drive. This can be done with external and internal Hard drives. The first method is to use your system’s RAM as a hard drive cache. For this, you can use software like ImDisk Toolkit and PrimoCache.
Another way is to use SSD as a hard drive cache. Windows Systems supporting Intel SRT can use the Intel Rapid Storage Technology software. In this software, you can assign and configure the SSD as a cache for your hard drive. You get the option to choose between the Write-Through and Write-Back methods for caching.
To use SSD as a hard drive cache, you can also use third-party software like PrimoCache and ExpressCache. You can easily customize the total cache size as per the requirements and remove it as well.
External Caching is pretty helpful but using the right methods is important to ensure data integrity. Because there is a layer of software doing the caching process, it is important to use the right software. It is good if you enable caching using the Intel SRT method. However, there are many other software that you can find on the internet.
Doing this could be tricky if you are doing it for the first time. However, you can find many tutorials on the internet for your specific operating system. So, make sure to perform it with proper care.
Conclusion
Hard Drive caching is important in improving hard drive performance. Although hard drives are almost replaced by solid state drives as the primary drives in the system if you have some applications for hard drives, it is good to go for cached hard drives.
I hope this helps!