The fundamental difference lies in the processing architecture. HBAs (Host Bus Adapters) act as simple passthrough devices that transfer SCSI/SATA commands directly between the host system and storage devices. RAID controllers, however, implement complex storage virtualization layers.

// Example showing HBA raw device access in Linux
int fd = open("/dev/sdc", O_RDWR | O_DIRECT);
ioctl(fd, BLKFLSBUF, 0); // flush buffer cache

Modern HBAs like the LSI 9211-8i you mentioned often include "RAID on HBA" features, creating confusion. These are typically software-assisted RAID implementations that still rely heavily on host CPU cycles, unlike dedicated RAID controllers with:

• Dedicated XOR processors for parity calculations
• Battery-backed write cache (BBWC)
• Non-volatile cache protection

When developing storage-intensive applications, the choice affects your I/O patterns:

// Bad practice for RAID arrays - 4K random writes
for (int i=0; i<1000; i++) {
    pwrite(fd, buf, 4096, random() % disksize);
}

// Optimized for RAID - sequential 1MB writes
const int chunk = 1024*1024;
posix_memalign(&buf, 4096, chunk);
for (int i=0; i<1000; i++) {
    pwrite(fd, buf, chunk, i*chunk);
}

Monitoring tools must account for the controller type:

# HBA health check
smartctl -a /dev/sda

# Hardware RAID status (MegaCLI example)
MegaCli -LDInfo -Lall -aAll
MegaCli -PDList -aAll

Applications interacting with storage should handle both scenarios:

int is_hardware_raid() {
    struct stat st;
    return (stat("/proc/mdstat", &st) != 0) ? 1 : 0;
}

void configure_io_scheduler() {
    if (is_hardware_raid()) {
        system("echo deadline > /sys/block/sda/queue/scheduler");
    } else {
        system("echo noop > /sys/block/sda/queue/scheduler");
    }
}

In our PostgreSQL cluster implementation, we found:

In storage architecture, HBA (Host Bus Adapter) cards and RAID (Redundant Array of Independent Disks) controllers serve distinct but sometimes overlapping purposes. An HBA primarily functions as a passthrough device that connects host systems to storage devices without processing the data, while a RAID controller manages disk arrays with additional processing capabilities.

# Example showing HBA vs RAID in Linux device listing
# HBA mode (JBOD)
$ lsscsi
[0:0:0:0]    disk    LSI     9211-8i          -      /dev/sda

# RAID mode
$ lsscsi  
[1:0:0:0]    disk    LSI     MegaRAID SAS     -      /dev/sda

The LSI 9211-8i you mentioned perfectly illustrates the convergence - it can operate in either mode through firmware:

• IT Mode: Pure HBA functionality (Initiator Target)
• IR Mode: Integrated RAID functionality

When building storage-intensive applications, consider these benchmarks:

# Python disk performance test snippet
import time
import numpy as np

def test_io(device):
    start = time.time()
    # 1GB random data write
    np.random.bytes(1024**3).tofile(device)
    return time.time() - start

# Typical results:
# HBA direct: 2.1s
# RAID5: 3.8s (due to parity calculation)

Modern cards often support mode switching through utilities like:

# MegaCLI example for mode checking
$ ./MegaCli -AdpGetProp -EnableJBOD -aALL

Adapter 0: JBOD: Enabled

# To switch modes (caution: requires reboot)
$ ./storcli /c0 set jbod=off

For developers working with direct device access:

// C example showing raw device access differences
#include 
#include 

void read_sector(int fd, unsigned long lba) {
    lseek(fd, lba * 512, SEEK_SET);
    char buffer[512];
    read(fd, buffer, 512);
    // HBA: Direct disk access
    // RAID: Virtualized LBA mapping
}