Data Storage Solutions

Posted Posted by Patrice Guay in Web hosting     Comments No comments
Apr
3

There are three main technologies for data storage on hard disk:

  • local storage (DAS)
  • storage on a standard network (NAS)
  • storage on a specialized network (SAN)

Each technology has strengths and weaknesses. While the local storage is the most widespread and has a high level of performance, network storage offers the possibility to share data between different servers. This last feature is increasingly sought either to synchronize data between different servers, to consolidate disk space or to enable advanced virtualization architectures.

Hard disks

In recent years, the size of hard drives has increased rapidly. Storage capacity of several terabytes is no longer expensive especially if storage space is created with SATA drives. However, the use of SATA drives to provide storage space may result in poor I/O performance. The use of SAS drives with a rotational speed of 15000 rpm instead of SATA drives at 7200 rpm provides up to two times higher I/O performance. SSD drives can be used to reach even higher I/O performance.

The table below shows the basic performance of different types of hard drives in terms of MB/s and IOPS (Input/Output Operation per Second). These data, collected from tom’s hardware website, may be handy to evaluate the performance level of a data storage solution :

For a database server, high I/O performance is desirable while required disk space is usually low. Small-sized SAS or SSD drives are more useful than SATA drives in this case. For file servers, high throughput is recommended especially if large-sized files are served (music, videos, etc.).

Furthermore, the discs can be arranged in a RAID configuration to achieve a performance level higher than that offered by a single disk.

DAS (Direct Attached Storage)

Local storage matches the disks installed in a server. This is obviously the most widespread type of storage since most servers, although they may be connected to a network storage system, access files from their operating system through local disks. Servers booting directly from a SAN are an exception to this rule since they can operate without local disks.

DAS is very efficient because disks are connected to the server processor via the built-in motherboard controller or an hardware RAID card. It is therefore a broadband and exclusive connection as it is not shared with other servers.

NAS (Network Attached Storage)

A storage system on a standard network share files via an IP network. These file sharing protocols are usually offered:

  • CIFS : Common Internet File System (natively on Microsoft Windows operating system)
  • NFS : Netowork File System (natively on Linux operating system)
  • AFP : Apple File Protocol (natively on Apple Mac OS X operating system)
  • WebDAV : Web-based Distributed Authoring and Versioning (HTTP protocol extension)

A simple file server may be converted into a NAS storage system. A portion of its local storage is then made ​​available to the other networked servers. Commercial solutions are also available and can provide additional functionality:

  • redundancy for the core system components (controller, network connectivity, electrical power)
  • optimization of file sharing protocols
  • caching of frequently accessed files
  • web-based management console

The performance of a NAS system is affected by several factors:

  • Type of disk drives (SATA, SAS or SSD)
  • RAID configuration of disk drives
  • Quantity of disk drives
  • Network connectivity
  • Type of shared files

The level of performance for a NAS solution depends on the limiting factor. For example, a set of sixteen (16) SATA drives in RAID 10 can offer a data throughput above 1 Gb/s. By cons, if these discs are placed in a NAS system with a 1 Gb/s network connectivity, the system performance can not exceed 1 Gb/s because of insufficient network connectivity. The limiting factor is then network connectivity. By using a 10 Gb/s network connectivity, system performance will be increased. The improvement of a factor other than network connectivity will have virtually no effect on system performance.

SAN (Storage Area Network)

A storage solution on a specialized network (SAN) uses iSCSI or Fibre Channel protocols to share storage space. In the case of a NAS, the storage resource is directly connected to the IP network while in the case of a SAN, storage space is available at the block level to the server file system. Each server sees the disk space on a SAN as its own hard drive. Traffic on a SAN follows similar conventions to those in force during communication with a local storage system. A SAN volume connected to a server can be formatted just like a local disk can be. This is obviously not possible in the case of a NAS volume.

In recent years, the iSCSI protocol has become increasingly attractive. The Fibre Channel protocol still exists, but tends to disappear in favor of the iSCSI protocol. Various reasons explains this phenomenon:

  • compatibility with standard IP network equipment
  • availability of 1 Gb/s and 10 Gb/s connectivity
  • low cost of IP network equipment (cables, switches, routers)
  • similarity of skills needed by network administrators

A SAN can meet some special needs:

  • Creating a Microsoft Windows cluster (ActiveDirectory, SQL, Exchange, etc.) to obtain an high level of redundancy
  • Allowing seamless migration of machines between servers in a virtualization solution (VMware, Xen)
  • Replicating a database between to distant locations
  • Consolidating storage space for a large quantity of servers
  • etc.

Apart from these specific needs, a NAS solution can usually reach a similar level of performance at a lower cost.

Conclusion

The conventional DAS storage solution (local hard drives) offers a high level of performance. The cost of this solution is also lower than that of NAS and SAN network storage solutions. For your network storage needs, the NAS allows sharing of files between different servers while a SAN solution makes available storage space at the block level.

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