RAID controller

[martixy]

What exactly does one of these do? And why are they so expensive?

Feel free to go as highly technical as you are able, we'll sort the fallout in the aftermath.

 

[dac7nco]

Hardware RAID controllers have a specialized CPU for parity calculations & interface microcode, have dedicated cache memory and a battery backup to keep the most recent writes in case of a power failure. Think of it as a specialized computer which does nothing but handle disk management and I/O. Each manufacturer has its own BIOS & firmware, and performance differs greatly. Most have SFF-8087 connectors which can either break into four SATA/SAS channels each or link directly with an internal enclosure, although some cheaper models have individual SATA connectors. (Example: an Areca 1680ix-24-4G can manage 24 SAS/SATA drives, 4GB of dedicated memory and a dual-core Intel CPU specialized for SAS I/O.)

The first really successful RAID controllers were probably the SCSI Adaptec 2940-series.
There is probably a huge markup for the cost of hardware RAID controllers.

Daimon

 

[martixy]

Ok...
So what does handling disk management and I/O entail and how much throughput goes through it that it would require so much dedicated compute power?

 

[Rubycon]

Hardware RAID controllers have a specialized CPU for parity calculations & interface microcode, have dedicated cache memory and a battery backup to keep the most recent writes in case of a power failure. Think of it as a specialized computer which does nothing but handle disk management and I/O. Each manufacturer has its own BIOS & firmware, and performance differs greatly. Most have SFF-8087 connectors which can either break into four SATA/SAS channels each or link directly with an internal enclosure, although some cheaper models have individual SATA connectors. (Example: an Areca 1680ix-24-4G can manage 24 SAS/SATA drives, 4GB of dedicated memory and a dual-core Intel CPU specialized for SAS I/O.)

The first really successful RAID controllers were probably the SCSI Adaptec 2940-series.
There is probably a huge markup for the cost of hardware RAID controllers.

Daimon

2940 family were not RAID hosts just SCSI controllers.
Probably the most widely known ones of the time were the AMI MegaRAID family. LSI bought AMI a while ago. DPT was purchased by Adaptec. I belived ICP Vortex was too. Mylex was acquired by LSI. The Mylex ExtremeRAID2000 was decent for its time. (U160 SCSI) I did prefer the MegaRAID Elite/Enterprise 160 controllers later on as they were more compatible with a wider variety of boards, etc.

There are many others from hp/IBM etc. as well. Dell rebrands LSI products in their PERC line. Most enthusiasts and homebrew server builders will use Areca or LSI. 3Ware is somewhat popular too. Adaptec is in the game as well and their support and compatibility is pretty good.

As for dedicated processing it's chiefly for RAID with parity (RAID3/5/6/50/60 etc.). These processors can offload XOR calculations and increase write throughput. Today's processors (sort of) negate the need for a dedicated XOR processor however the hosts are intelligent and feature management and alerting capabilities that are just not possible with software only solutions. Combined with larger write back / delayed write cache with battery backups and you have a solid storage solution independent of the operating system to manage, etc.