What is a RAID Controller Card? Why do I need one and what does it do? Why not use a software RAID?

What is a RAID Controller PCIe Card? What is BBU? How do I choose the right RAID Card? https://www.span.com/search/raid_space_controller/5-

One of the basic components of a storage system is the host bus adapter (HBA) which provides connectivity between a server and a storage device. Though HBAs do not inherently provide RAID functionality, they can be used with software RAID for some degree of redundancy.

“Software RAID” simply refers to configurations where the RAID task is executed using the processor on the server. In other words the software RAID code utilizes the calculating power of the computer’s CPU, sharing the same computing power used by the operating system and associated applications.
Software RAID can only consistently allow for RAID levels 0, 1, and 10 – remember back to the RAID levels we discussed in our introduction to RAID.

“Hardware RAID”

In contrast to software RAID, “hardware RAID” involves the RAID task being executed by the processor of a dedicated card or RAID controller. Generally speaking hardware RAID is superior to software RAID, with several notable advantages including:
1. Full range of RAID configuration levels (RAID 0, 1, 5, 6, 0+1, 10, 50, 60, etc.)

2. Dedicated processor and memory to execute the RAID application, offloading the task from the server processor and improving performance

3. More features which are not possible with software RAID (e.g. power failure protection, caching, etc.)

Hardware RAID can be integrated into the motherboard, but typically the best hardware solutions call for an add-on card which connects to the motherboard and storage drives, typically through PCI-e slots.
Choosing a RAID Card
Add-on RAID cards are generally the most flexible, scalable and best-performing hardware setup as multiple storage and RAID arrays can be added without decreasing the performance of the host system. This becomes even more important with RAID configuration levels that involve calculating parity (RAID 5, 6, 50, 60).
There are a few things to consider when looking at different RAID cards:
Onboard memory / cache - The memory is used for read and write cache which improves the performance of the storage. The basic rule when it comes to cache is buy as much as you can afford. The more cache you have the better the performance of the disks will be as data can be written to the memory if the disks aren't in the correct position.

Battery backup unit (BBU) - t doesn't power the disks, it just keeps the data in the cache for (in this case) up to 72 hours until you bring the machine back on line. When you power the machine back up it will write the contents of the cache back out to the disks.

All it does is protect against a power failure. If (for some reason) the machine loses power without cleanly flushing the data out to disk the battery keeps the cache contents alive until you can restart the machine.

It is not a UPS for disks, as the disks could be in an external disk array, or even on a different power circuit. Even a UPS could fail.


RAID levels supported – As discussed, most MID-RANGE cards can handle typical RAID like RAID 0, 1, 5, 6 and 10. But once you need larger arrays like RAID 50, 60 or multiple Arrays In A Single Server, You Will Need To Buy Higher End Cards.

Number of ports – Low to mid range cards arrive with SATA only ports on board and more enterprise cards arrive with SAS / SATA ports. If you buy a KIT version, it will arrive with the fan out cables for SATA/SAS, or you can buy the card BARE and buy more economical cables as needed

Brand (there are only a few major ones) – LSI, Adaptec, Areca, etc.

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