What is difference between scsi and sata and ide controllers

Think of IDE → SATA → SCSI → NVMe as an evolution of storage technologies.

 

Feature	IDE (PATA)	SATA	SCSI	NVMe
Era	Very old	Desktop/server standard	Enterprise servers	Modern SSDs
Speed	Slow	Faster	High performance	Fastest
Queue Depth	1 command	32 commands	Thousands	64K queues × 64K commands
Multiple Devices	Limited	Moderate	Excellent	Excellent
Typical Use	Old PCs	HDDs/SSDs	Enterprise servers/SAN	Modern SSDs, Azure v5/v6/v7
Device Names in Linux	/dev/hda	/dev/sda	/dev/sda	/dev

 

1. IDE (Integrated Drive Electronics)

Old desktop technology.

Limitations

• Very low performance

• Limited parallelism

• Few devices per controller

 

2. SATA (Serial ATA)

Replaced IDE in desktops and laptops.

OS--> SATA Controller --> SSD/HDD

 

Benefits over IDE

• Faster
• Simpler cabling
• Hot-plug support
• Better reliability

Still common for:

• Desktop SSDs
• HDDs
• Low-cost servers

 

3. SCSI : Small Computer System Interface.

 

Designed for enterprise storage.

OS--> SCSI Controller --> Many Disks

 

Benefits

• Supports many disks
• Better error handling
• Higher queue depth
• SAN integration
• Enterprise features

 

This is why VMware, Hyper-V and Azure traditionally expose storage through a virtual SCSI controller.

 

4. NVMe : Non‑Volatile Memory Express

Built specifically for SSDs.

 

OS --> NVMe Controller --> Flash Storage

Major advantages

• Very low latency
• Much higher IOPS
• Better CPU efficiency
• Massive parallelism

 

This is why Azure is moving newer VM sizes from SCSI to NVMe. The storage remains remote Azure Managed Disk, but the guest OS communicates through an NVMe controller instead of a SCSI controller

 

Simple Analogy

Imagine a highway:

• IDE = 1-lane road
• SATA = 2-lane road
• SCSI = 8-lane highway
• NVMe = 100-lane expressway

 

When many I/O requests arrive simultaneously, NVMe can process far more requests with lower latency.

 

Why VMware Still Uses SCSI?

Most operating systems support SCSI universally.

Advantages:

• Excellent compatibility
• Stable and mature
• Works with Windows, Linux, Unix
• Easy migration between platforms

 

 

The controller interface and the actual storage media are two different things

SSD can be connected through either a SCSI controller or an NVMe controller. SSD does not automatically mean NVMe.

NVMe can process many more I/O requests simultaneously.

 

 

 

[root@RHEL8 ]# sudo lshw -class disk -class storage

  *-scsi:0                 

       physical id: 7

       logical name: scsi1

  *-scsi:1

       physical id: 8

       logical name: scsi0

     *-disk:0

          description: SCSI Disk

          product: Virtual Disk

          vendor: Msft

          physical id: 0.0.0

          bus info: scsi@0:0.0.0

          logical name: /dev/sdb

          version: 1.0

          size: 64GiB (68GB)

          capabilities: gpt-1.00 partitioned partitioned:gpt

          configuration: ansiversion=5 guid=1121c682-1627-4ef1-bc0f-7eeaa7dd31a4 logicalsectorsize=512 sectorsize=4096

     *-disk:1

          description: SCSI Disk

          product: Virtual Disk

          vendor: Msft

          physical id: 0.0.1

          bus info: scsi@0:0.0.1

          logical name: /dev/sdc

          version: 1.0

          size: 75GiB (80GB)

          capabilities: partitioned partitioned:dos

          configuration: ansiversion=5 logicalsectorsize=512 sectorsize=4096 signature=a2aeecc8

 

 

In bus info: scsi@0:0.0.0 is the SCSI addressing format.

scsi@Host:Channel.Target.LUN  OR  [Host:Channel:Target:LUN] --> HCTL

 

Field	Value	Meaning
Host	0	First SCSI controller
Channel	0	Channel on controller
Target	0	Target device ID
LUN	0	Logical Unit Number

 

[root@RHEL8 naveen]# lsscsi

[0:0:0:0]    disk    Msft     Virtual Disk     1.0   /dev/sdb

[0:0:0:1]    disk    Msft     Virtual Disk     1.0   /dev/sdc --> 1st SCSI controller with LUN 1

[1:0:0:0]    disk    Msft     Virtual Disk     1.0   /dev/sda  --> 2nd SCSI controller with LUN 0