What is a Hard Disk Cache and its importance?

Hard Disks are relatively slow when it comes to 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 primary purpose is to store recently or frequently accessed data, thereby improving 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 essential files, such as cookies, in the cache to improve application performance.

The hard disk cache is generally composed of DRAM cache due to its high speed and efficiency. It is also used in DRAM SSDs. In hard drives, the primary purpose of this cache is to give an artificial performance boost.

Without a cache, a hard drive can significantly impact the overall system performance. Therefore, it is a crucial factor when selecting a new hard drive. Let’s discuss everything in detail.

Purpose of Hard Drive Cache

The primary role of the hard drive cache is during the read operations. When the host requests any data, the hard drive controller first checks the cache to see if the data is already present there. There is a process called prefetching where the drive may predict which data might be requested next and load it into cache ahead of time to speed up future access. 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.

Another primary purpose of hard drive cache is write caching. It temporarily holds data to be written to the disk, allowing the system to move on without waiting for the slow physical write operation to complete.

1. Cache Population

If the data requested by the host isn’t available in the cache, it is called a cache miss. The hard drive must access the data from the platter, but it does not send the data directly to the system; instead, it saves a copy in the cache. In addition to this data, some related data is also stored in the cache.

Not all data can be stored in the cache due to its limited size. Hard drives often employ the LRU (Least Recently Used) algorithm to manage this restricted space and select the most suitable type of data to store in the cache. LRU continually replaces old data with new data as the system requests it.

For cache population, the controller also performs read-ahead caching, which involves reading and storing more data than requested to facilitate further improvements. Additionally, there are adaptive algorithms that learn from usage patterns and prioritize frequently used 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.

2. Speed up write operations

Write caching is another primary purpose of the hard drive cache. In this process, the hard drive cache serves as a buffer to temporarily store incoming write data. This improves the perceptual write speed, and when the drive is idle, the stored data is written to the platter for permanent storage.

The write cache enables the CPU to be freed from write operations almost instantly. 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, rather than being written 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, data is written to both disk and cache. It doesn’t offer many performance benefits. In Write-Back caching, the data is written to disk later; thus, the write speed is improved.

3. 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 achieved by efficiently utilizing the mechanical platters, employing sequential data writing as discussed above.

Real-World Benefits of Caching in Hard Drives

1. Improved Performance

The first real-world benefit of hard drive cache is improved performance in both 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 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 battery-powered 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 programs 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 to perform better.

4. Better performance in high-load situations

In server and data center 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 prevent slowdowns and crashes caused by 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, such as databases and real-time logging systems, this can be highly beneficial.

There are many additional benefits to having a cache with your hard drive, including support for larger data sets and improved 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 inexpensive drives come without any caching mechanism. These drives have some significant disadvantages compared to 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 entirely written. The latency is increased because the platters will take time to locate the requested data.

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, resulting in performance degradation.

The multitasking performance decreases, and power efficiency is reduced—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 primary 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 an 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 according to your requirements and remove it as needed.

External Caching is pretty helpful, but using the proper methods is essential to ensure data integrity. Since a layer of software handles the caching process, it is crucial to use the correct software. It is beneficial to 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. Therefore, ensure that you perform it with proper care.

Conclusion

Hard Drive caching is crucial for enhancing hard drive performance. Although solid-state drives are replacing hard drives as the primary drives in the system, if you have some applications that require hard drives, it is beneficial to opt for cached hard drives.

I hope this helps!