High Capacity

Data Storage Systems provide storage facilities to servers by highest virtual capacity, performance, and availability. In an IT structure equipped with data storage systems, severs do not locally store data, instead, data storage system takes over all storage needs while assuring continuous service and high availability.

One of the key features of a SAN storage is providing virtual capacity to servers, also known as data provisioning. This facility enables allocating logical storage capacity to users more than physical storage capacity, regarding the fact that storage users usually do not use all their logical capacity. In a SAN storage, all the storage complexities including redundancies, data tiering, and caching mechanisms are transparent in the user side and totally handle by storage controllers.

The storage capacity is one of the key features for classification of data storage system. The storage capacity should be provided by assuring very low chance of Data Loss and Data Unavailability:

No Data Loss
A data storage system should assure almost zero chance of Data Loss by employing redundancy mechanisms in storage components such as disk array and controllers, alongside system level redundancies such as backups, snapshots, and mirroring. For example by using RAID mechanism, the disk array can tolerate one or more disk failure and the user data is reconstructed on a brand-new disk using other operating disks.
No Data Unavailability
Continuous data availability is one of the most important features of a data storage system. High availability is provided by employing high dependable designs in both hardware and software stack, from storage controllers, interconnections, power supply, and storage arrays, to operating system and storage management software.
Disk types used in data storage systems

Disk drives are the most important components of a data storage system, appeared in different types:

SAS Disk
SAS disks are the most reliable HDDs, having more tolerance to harsh environment. These disks usually appear with lower capacity and higher performance compared to other types of HDDs. The Bit Error Rate (BER) of SAS disks is typically reported as 10-16, meaning that one of 1016 bits of data is prone to bit error that is a comparably good value. The Mean Time to Failure (MTTF) of SAS disk is typically reported a 1.6 Million hours, meaning that the expected lifetime of a SAS disk is 1.6 Million hours or 182 years. However, these values highly depend on the brand and type of the disk. Moreover, the disk failure behavior in the field does not necessarily follow the MTTF reported by manufacturers. The SAS controllers have a more versatile command set compared to SATA and NL SAS. The capacity of SAS disks is usually between 600GB and 1TB.
NL SAS disks
NL SAS disks provide lower reliability and performance compared to SAS disk, while performing better than SATA disks. NL SAS disks have an interface similar to SAS disks that enables using these disks instead of SAS disks. Similar to SAS disks, these disks come with dual channel, but their performance and reliability characteristics are similar to SATA disks. BER of NL SAS disks is typically reported as 10-15 and their MTTF is typically reported as 1.2 Million hours (136 years).
SATA disks
These disks are attributed by high capacity, low price, low speed, and low reliability compared to other HDD types. Due to their lower reliability and price, these disks are employed in less demanding applications such as archiving or storing cold data. SATA disks are usually working in 5400 and 7200 RPM.
SSD disks
Solid State Drive (SSD) disks are already the fastest storage media in the market. Unlike HDDs, SSDs have no mechanical part, providing more tolerance to mechanical shocks and better durability. The read/write performance of SSDs better than HDDs by orders of magnitude, while having much lower power consumption compared to SAS and SATA disks. The major shortcomings of SSDs are comparably high cost and limited number of writes.
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