Although both server-side caching and RAID Controller Caching Memory are both performed within the actual server, server-side caching typically refers to a software-based method of cache at the scsi controller. This method is an element of software which is either located on the hypervisor layer, or inside the physical machine. The software is able to automatically store the most frequently accessed data or any data it has decided to store for storage to the drive form factor SSD or PCIe SSD mounted on host servers. This reduces the load of the network storage as well as those sharing the storage.
What exactly is RAID Controller Caching?
The RAID controller is generally an electronic device that is placed on a server. It can connect to multiple drives and then aggregate them to protect data using one or more of the many RAID methods (RAID 0 1, 10, being the most commonly used). Modern RAID controllers can also offer additional functions such as snapshots, compression or reduplication.
The controllers were always equipped with caching, however it was usually only a small cache (less than 64 MB) and was based on DRAM and not flash. More often, however, flash controllers are now adding the capability of supporting either a flash drive on the motherboard or a module to dramatically increase the cache memory they are able to benefit from. This latest model of RAID controllers is known as the Cached RAID Controller.
When deciding on which caching technology to employ, companies are frequently confronted with the choice of two choices. While both serve a similar purpose, speeding up the speed of hot data offer distinct differences that could affect the business.
The primary distinction is the cache flexibility. The majority of Cached RAID Controllers demand that the storage for flash be integrated into the controller. Although this allows the controller with connection to the storage, it also limits the amount of options that the storage manager can choose from. There is often no option that the flash has to come from the controller’s vendor.
A server-side, software-based cache, however, is typically able to work with any kind of flash storage that’s accessible to the server. This could mean an SSD that is PCIe or a drive with form factors SSD within the server. It also implies that the same software could create multiple caches on different devices, regardless of the location. It is also possible to create a shared SSD that is integrated into the SAN. It could then utilize that cache to handle every I/O streams (block or file) which the system communicates.
Any Cached RAID Controller will only store volumes it directly manages, and this is the only way to get rid of a fiber channel-attached or network-attached storage device.
Although there could be some reduction in latency when using the RAID controller to cache, however the benefits is minimal when as compared to a software-based cache using the PCIe SSD. If a drive form factor or SAN connected flash is utilized by the caching software, the effect on latency will be minor and barely noticed in the majority of applications. With the capability to store multiple types of volume and places software caches, it is possible to establish a hierarchy of caching to help balance the cost of investment against the actual acceleration provided.
One of the main benefits of the flexibility of caches in software-based server-side caching is the amount of capacity that can be assigned to the caching feature. A cache will only be effective in the event that the majority of the hot data is stored in the cache, not the hard disk. A cache’s size directly affects the ratio of hit/miss. Although they are larger than the predecessors, they are still smaller than their DRAM caches the cached controllers generally only support a couple of on-board cache modules. Software-based caches aren’t subject to limitations in terms of functionality since they are able to access and combine flash storage using PCIe Drive Form Factor SSDs, and shared SSDs.
Another approach to increase the ratio of hit-and-miss in caches can be to become more savvy in the way that cache storage is utilized. Although limitless capacity is great however, it can be costly. It is ideal to find a balance between the size of the cache and the cache’s ability to be intelligent.
The most effective method to allow the cache to attain this insight is to be aware of the applications it is speeding up. In a virtualized environment, this means being able to restrict VMs to specific cache volumes, or attaching the whole VM to the cache. This also implies having an understanding of how the environment presents information and how it can be accessed.
One of the benefits of the caching RAID configuration is the fact that there will be any additional programs to download, other than those drivers that are required by the controller. A server-side cache that is based on software however is a requirement to install applications on the server. What is “easier” a controller is to install is contingent upon the specific situation. For instance, many IT managers don’t anticipate the necessity of cache prior to server deployment. In reality, the majority of instances will need to gradually to add cache within the time frame following the initial implementation. This means the initial RAID controller will have to be replaced by an updated cached controller. This involves shutting down the server before installing the new controller and, if necessary, the installation of a new driver.
It’s similar to the software cache that requires installation, however it would not require shutting down and opening of servers. In many cases the reboot isn’t necessary.
The only benefit the cached controller could have is if the server is being ordered with the RAID controller cached, and there was no requirement to store network volumes. If not, the use of the cached RAID controller might be more challenging.
Performance Effect of Cache
Another advantage theoretically of an RAID controller that is a cached RAID controller is that the actual processing is performed “on-board”. This means that neither host CPU nor memory resources must be utilized for the necessary data analysis to determine what data should be kept in the cache and what should not. They are also utilized to carry out the actual copy of data to the disk layer. Onto that layer.