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NAS or
iSCSI
Selecting a Storage
Systems
(Extracted from OPEN-E
whitepaper)
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Introduction to storage
systems
Direct Attached Storage is a system of hard
drives addressed directly via system buses within the computer (IDE,
SCSI); the network interface is managed by the operating system. As
these buses can only bridge short distances within the decimeter
range, DAS solutions are limited to the respective computer casing.
Depending on the bus type, DAS systems are also restricted to a
relatively small number of drives - Wide-SCSI achieves the maximum
of 16 directly addressable drives. Due to these limitations and the
need for more flexible storage, the importance of DAS is declining.
Although DAS in terms of terabyte is still growing by 28% annually,
the need for storage is increasingly being covered by networked
storage like NAS and iSCSI systems. NAS systems are generally computing-storage
devices that can be accessed over a computer network (usually
TCP/IP), rather than directly being connected to the computer (via a
computer bus such as SCSI). This enables multiple computers to share
the same storage space at once, which minimizes overhead by
centrally managing hard disks. NAS devices become logical file
system storage for a local area network. NAS was developed to
address problems with direct attached storage, which included the
effort required to administer and maintain server farms, and the
lack of scalability, reliability, availability, and performance.
They can deliver significant ease of use, provide heterogeneous data
sharing and enable organizations to automate and simplify their data
manag Storage Area Networks (SAN), which also include
iSCSI, are distinguished from other forms of network storage by
using a blockbased protocol and generally run over an independent,
specialized storage network. Data traffic on these networks is very
similar to those used for internal disk drives, like ATA and SCSI.
With the exception of SAN file systems and clustered computing, SAN
storage is still a one-to-one relationship. That is, each device (or
Logical Unit Number (LUN)) on the SAN is owned by a single computer
(or initiator). SANs tend to increase storage capacity utilization,
since multiple servers can share the same growth reserve. Other
benefits include the ability to allow servers to boot from the SAN
itself. This allows for a quick and easy replacement of faulty
servers since the SAN can be reconfigured so that a replacement
server can use the LUN of the faulty
server. This white papers aim is to help system
administrators decide between the two storage technologies NAS and
iSCSI. Both technologies were developed to help cover the
exponentially increasing need for storage capacity by means of
external, scalable storage devices that can be networked if
necessary. In any company, the use of storage solutions
will depend on a number of different
factors:
Within these basic considerations, system
administrators must decide which technology and which products are
best suited to meet their needs. A NAS server is a specialized appliance
optimized for file serving, i.e., storing, retrieving, and serving
files. Typical applications include:
NAS systems offer a number of
advantages:
What are Some Disadvantages of
NAS? NAS has the following
disadvantages:
Typical iSCSI
applications iSCSI stands for Internet Small Computer System
Interface, a technology that extends the Internet Protocol to
Storage Area Networks (SAN). A primary usage of iSCSI is instant disk space.
With no server downtime or re-boot required you install the
initiator driver on f.e. the Windows machine, map the storage to the
disk then allocate the desired disk capacity and format it under
disk manager. An iSCSI SAN can utilize an existing Gigabit
network to serve up storage and is therefore particularly appealing
for small and medium-sized businesses. It leverages the investment
in the networking infrastructure and also the storage management, as
most IT professionals understand TCP/IP. Adding Fibre Channel
storage involves extensive training on mapping and managing
storage. Of course NAS systems can also be implemented
via iSCSI, but from a financial point of view this only makes sense
if an iSCSI-based storage solution is to be set up anyway. On the
other hand, iSCSI targets can also extend the storage capacity of a
NAS server - although this requires an iSCSI initiator on the NAS
server.. Typical iSCSI applications
include:
Advantages of
iSCSI iSCSI systems offer a number of
advantages:
What are Some Disadvantages of
iSCSI? iSCSI stands for Internet Small Computer System
Interface, a technology that extends the Internet Protocol to
Storage Area Networks (SAN). The demands of accommodating SCSI commands and
SCSI data packets in TCP/IP packets require extensive hardware
resources: CPU performance should be at least that of a 3 GHz
Pentium processor, Gigabit Ethernet (GbE) should accordingly be used
as a network interface, and the RAM requirement is also
significant. For sharing iSCSI targets with multiple
initiators, additional server or specific (client) software for
shared data access is required. Known providers of SAN data sharing
software are Adic, Sanbolic, IBM, Polyserve, Dataplow and
SGI. As iSCSI is an underlying technology to the OS
and application, anything that an organization currently has can be
used. On the other hand this means that extra licenses for OS and
software applications might be needed. Comparing to NAS, an iSCSI Target is not a
standalone device and an additional host server is
necessary. For sharing centralized storage pool disk among
heterogeneous OS requires additional sharing
software. In iSCSI appliances mechanisms for f.e. backup,
data synchronization and data replication are not integrated and
must be configured. Comparing to NAS, iSCSI behaves like a local
hard drive in the network. Network Attached Storage (NAS) is the obvious
choice for a storage solution wherever the main focus is on storing
and archiving files and shared access to these over a network even
from different client operating systems. Small and medium-sized
businesses, typing pools, legal or agency offices, and even end
users with large amounts of multimedia files will find an affordable
storage solution for their needs in
NAS. For storing database systems - other than
SQL-based database systems - on a network, NAS is however not a
feasible solution. For requirements of this type the industry has
developed the Storage Area Network (SAN) technology, which can often
be implemented using iSCSI components. Advantages of iSCSI: An
IP-based SAN allows administrators to use their familiar management
tools and security mechanisms and rely on their existing know-how.
However, iSCSI only makes sense in connection with a fast LAN
infrastructure: At a throughput of approximately 120 Mbyte/s, the
performance of a 1 Gbit Ethernet will be sufficient for database
applications for approximately 100 users (data volume: approx. 15
MByte/s). Only high-end storage systems will require a 10 GbE
infrastructure. Somewhat inefficient since data transfer rides on
top of standard TCP/IP protocol. In contrast, SAN uses protocols
designed especially for data transfer (though the advantage
disappears if a server on the LAN is used to provide a file
interface to a SAN). |
