External Storage

For server setups (specially in production environments),external storage solutions are used instead of built in disks. Here is an overview of different types:

DAS (Direct Attached Storage)

• A DAS device is connected directly to a host (server).
• Given the direct connection is fast and performant
• For the Host OS, it is detected as a block device
• It is however dedicated to a single host

NAS (Network Attached Storage)

• A NAS device is located apart from the hosts and communicates via networks
• Storage traffic has to go always to the network which can make it “slow”
• For the host OS, the device is exposed as a folder via protocols like NFS (see Filesystems.) or CIFS
• Ideal for shared storage between different nodes, but not recommended for “critical” uses like DBs, or OS installation where the latency might be too much

SAN (Storage Area Network)

• A SAN device is located apart from the hosts and communicates via fiber-based dedicated connection
• For the Host OS, it is detected as a block device
• Internally storage is allocated to hosts as Logical Unit Numbers (LUNs), which represent sections of a shared storage pool presented as logical disks to the server.
• Much better performance as the other two