SAN (Storage Area Network) storage refers to a dedicated high-speed network used to connect servers to shared pools of storage devices like SSDs (solid state drives) or HDDs (hard disk drives). So SAN storage can utilize either SSDs or HDDs depending on the performance and cost requirements.
Some key questions answered in this article:
- What is SAN storage?
- What is the difference between SSD and HDD?
- What are the pros and cons of SSD and HDD SAN storage?
- When should you use SSD vs HDD SAN storage?
- What factors should you consider when choosing between SSD and HDD SAN?
What is SAN storage?
SAN (Storage Area Network) is a dedicated high-speed network that provides access to consolidated, block-level storage. It allows multiple servers to connect to shared storage devices like disk arrays and tape libraries.
The key advantage of SAN storage is that it separates storage traffic from general LAN network traffic, providing dedicated bandwidth for storage. This allows for faster data access. SANs also provide centralized storage and management, scalability, and data sharing between clustered servers.
Common SAN protocols include Fibre Channel (FC), Fibre Channel over Ethernet (FCoE), iSCSI, and InfiniBand. Storage devices are connected to FC switches or iSCSI switches that allow servers to access storage over the network.
SAN Components
The key components of a SAN include:
- Servers – The servers connecting to the SAN to access shared storage.
- SAN switch – FC switch or iSCSI switch that connects servers to storage devices.
- Storage devices – Disk arrays, JBODs, tape libraries etc. that provide consolidated storage.
- Cables – Fiber optic cables for FC or Ethernet cables for iSCSI.
- Host bus adapters (HBAs) – Server adapters providing ports to connect to the SAN.
- SAN management software – Monitors and manages SAN resources.
Difference between SSD and HDD
SSDs and HDDs are two different types of storage media that have quite different performance characteristics:
| Factor | SSD (Solid State Drive) | HDD (Hard Disk Drive) |
|---|---|---|
| Technology | Flash memory chips like NAND flash | Magnetic platters rotated by a spindle motor |
| Speed | Much faster, low latency | Slower performance, higher latency |
| Reliability | No moving parts, resistant to shock | Mechanical parts, prone to failure due to wear & tear |
| Price | More expensive per GB | Cheaper per GB |
| Capacity | Lower density, capacities up to 16TB | Higher density, capacities up to 18TB |
In summary, SSDs are faster, more reliable and resistant to shocks, while HDDs have larger capacities and are cheaper per gigabyte.
Pros and Cons of SSD SAN Storage
Pros
- High performance – SSDs provide much lower latency and higher IOPS which means faster data access for applications.
- Lower power usage – SSDs consume less power than spinning HDDs.
- Improved reliability – With no moving parts, SSDs are more resistant to failure or damage from shocks and vibration.
- Faster boot/restart times – Servers can boot faster from SSD storage.
- Noise reduction – SSD arrays generate no noise unlike the spinning platters in HDDs.
Cons
- Higher cost – SSDs are more expensive per gigabyte compared to HDDs.
- Lower capacities – Maximum SSD capacities top out at around 16TB while HDDs reach up to 18TB.
- Wear leveling needs – SSDs require wear leveling techniques to evenly distribute writes across memory blocks.
- Drive writes per day limits – SSDs have limits on how much data can be written per day before wearing out.
Pros and Cons of HDD SAN Storage
Pros
- Lower cost per GB – HDDs are cheaper per gigabyte compared to SSDs, allowing more storage capacity for the budget.
- Higher maximum capacities – HDDs are available in capacities up to 18TB, allowing massive SAN storage.
- Mature technology – HDDs have been used and improved for decades making them a stable, well-understood storage technology.
Cons
- Slower performance – HDDs have higher latency and lower IOPS, making them slower for demanding workloads.
- Higher power usage – The spinning platters and motors in HDDs use more electricity.
- More prone to failure – The mechanical parts in HDDs are subject to wear and tear, leading to higher failure rates.
- Vulnerable to shock/vibration – HDDs can be damaged by physical shocks and vibration.
- Noise – The spinning platters generate audible noise which needs to be dampened.
When should you use SSD SAN storage?
SSD SAN storage offers the best performance but is more expensive. Good uses cases for SSD SAN include:
- High performance databases – Fast response times to support high transaction databases like Oracle, SQL Server, MongoDB etc.
- Latency sensitive applications – Applications where latency directly impacts user experience and productivity.
- Frequent access data – “Hot” data that is frequently accessed benefits highly from SSD speed.
- Sequential write workloads – SSDs handle sequential writes better than random writes.
- Read intensive workloads – Reads are faster on SSDs than writes.
- Small dataset sizes – SSD capacities are sufficient for small databases or data warehouses.
The lower latency, higher IOPS and overall speed of SSD SAN storage make it ideal for workloads that require fast storage performance.
When should you use HDD SAN storage?
While slower than SSDs, HDDs offer much higher capacities at lower cost. Good use cases for HDD SAN storage include:
- Archival/backup data – Rarely accessed “cold” data like archives and backups.
- Large datasets – Big Data analytics, data lakes and data warehouses storing massive amounts of structured, unstructured data.
- Media libraries – Storing large volumes of rich media like videos, images.
- Low IOPS requirements – Workloads that don’t require high IOPS performance.
- Sequential read workloads – Streaming/reading large files benefits from HDD sequential throughput.
- Low budget projects – HDD SAN provides substantial capacity at lower cost.
The high density and large capacities of HDD SAN storage make it suitable for large datasets, media libraries and archive data that doesn’t need ultra-fast performance.
Factors to consider when choosing between SSD and HDD SAN storage
Key factors to consider when deciding between SSD and HDD SAN storage include:
- Required performance – IOPS, throughput and latency needs of applications. SSD is faster while HDD provides capacity.
- Data accessibility – Frequency of data access. SSDs for hot data, HDDs for cold/archival data.
- Capacity requirements – Dataset sizes. SSD capacities are lower than HDD.
- Budget – SSD offers speed at higher cost. HDD provides affordable capacity.
- Power and cooling – SSDs consume less power and generate less heat.
- Physical size – HDDs allow massive capacity in small space via high density.
- Noise level – HDDs generate audible noise due to spinning platters.
- Reliability requirements – SSDs are more resistant to shocks and failure.
Analyzing the performance profile, capacity needs, power limitations and budget will help determine whether SSD or HDD SAN storage is more suitable. Hybrid SAN configurations can leverage both SSD and HDD storage tiers.
Sample SAN configurations with SSD and HDD storage
All-Flash SSD SAN
- 2 redundant FC SAN switches
- SSD storage arrays providing 50 TB total RAW capacity
- SSDs providing 250,000 IOPS and sub-millisecond latency
- 8Gb/s FC links between servers, switches and SSD arrays
- Ideal for transactional databases needing high performance
High Capacity HDD SAN
- Redundant iSCSI SAN switches
- Multiple JBODs with 18 TB HDDs providing 1.5 Petabyte total capacity
- HDDs providing 110,000 IOPS and 4-6 ms latency
- 10Gbps iSCSI links between servers, switches and JBODs
- Well suited for Big Data analytics and data lakes
Hybrid SAN with SSD and HDD Tiers
- Redundant FC SAN switches
- SSD storage array with 10 TB capacity and 180,000 IOPS
- HDD JBODs providing 220 TB additional capacity
- SSD tier for mission critical databases needing performance
- HDD tier for backups, archives and cold data
- Storage tiering optimizes hot data on SSD tier automatically
Hybrid SAN architectures provide the right media for the use case – SSD for performance and HDD for capacity and cost savings.
Conclusion
SAN storage can leverage either SSD or HDD devices to meet an organization’s needs. SSD SAN provides faster performance and lower latency but has lower densities and higher cost. HDD SAN offers massive capacities for affordably storing huge datasets but has slower IOPS and higher latency.
Key factors like required performance, capacity, budget, data access patterns and reliability requirements determine whether to use all-SSD, all-HDD or a hybrid SSD+HDD SAN architecture. Analyzing your workloads and data storage needs will help select the right media and optimize your SAN storage configuration.
