SAN ( Storage Area Network )
In information technology, a storage area network (SAN) is an architecture to attach remote computer storage devices (such as disk arrays, tape libraries and optical jukeboxes) to servers in such a way that, to the operating system, the devices appear as locally attached. Although cost and complexity are dropping, as of 2007, SANs are still uncommon outside larger enterprises.
NAS ( Network Attached Storage )
In contrast to a SAN, Network Attached Storage (NAS) uses file-based protocols such as NFS or SMB/CIFS where it is clear that the storage is remote, and computers request a portion of an abstract file rather than a disk block.
NAS network schema
Clustered NAS
A clustered NAS is a Network-attached storage solution which is using a distributed file system running simultaneously on multiple servers. The key differentiating factor of clustered NAS from traditional NAS is its ability to stripe data and metadata across the cluster nodes and storage subsystems, and provide access to the networked file system from any of the cluster nodes, unrelated to the actual location of the data. For this reason clustered NAS solutions are typically associated with virtualization.
VMSTAT ( virtual memory statistics )
vmstat (virtual memory statistics) is a computer operating system monitoring tool that collects and displays summary information about memory, processes, interrupts, paging and block I/Oinformation. By specifying the interval, it can be used to observe system activity interactively.
The vmstat tool is available on most UNIX and Unix-like operating systems, such as Linux. The syntax and output of vmstat often differs slightly between different operating systems.
Example:
#> vmstat 2 6 procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 2536 21496 185684 1353000 0 0 0 14 1 2 0 0 100 0 0 0 2536 21496 185684 1353000 0 0 0 28 1030 145 0 0 100 0 0 0 2536 21496 185684 1353000 0 0 0 0 1026 132 0 0 100 0 0 0 2536 21520 185684 1353000 0 0 0 0 1033 186 1 0 99 0 0 0 2536 21520 185684 1353000 0 0 0 0 1024 141 0 0 100 0 0 0 2536 21584 185684 1353000 0 0 0 0 1025 131 0 0 100 0 #>