Creating an iSCSI-based SAN
Overview
For businesses needing to consolidate and centralise storage there
has been only one viable solution thus far Fibre Channel. This
is changing as iSCSI is quickly becoming a mainstream technology
that can offer speeds approaching that of Fibre Channel for only
a fraction of the cost. Using off-the-shelf IP network products
and ATTO's iSCSI-to-SCSI bridges, you can create a low-cost, easy-toimplement
Storage Area Network (SAN).
iSCSI, which is the SCSI protocol
transmitted over the IP, is similar in functionality to networked
Attached Storage (NAS) in that you can simply hang your storage
directly on the network for all to access. The big difference
is that NAS protocols move data based upon file level transfers
while iSCSI uses block level transfers. Many database, tape backup,
and other applications that deal with large files such as imaging
and video benefit tremendously in performance with the ability
to do block level transfers.
This tech brief will describe
the components needed to build an iSCSI SAN and provide some explanation
on how to properly configure it.
IP SAN Benefits
More effective use of storage: By allowing for storage consolidation,
the servers can share a common pool of storage. This effectively
reduces the number of servers with unused capacity and bandwidth
by allowing the IT administrator to better balance the load. It
also reduces license and hardware costs.
More efficient management
of storage: It is much easier and more cost effective
to manage a common pool of storage than many distributed direct
attach pieces of storage.
Higher availability and
simplified data protection: Through the use of redundant
data paths single points of failure can be easily and cost effectively
removed.
Faster backup and restore
time: Since iSCSI traffic is block-level, data can be
backed up faster than with traditional file-based backups. It
is also considerably more efficient to back up from a pool of
storage over the SAN.
Ability to easily scale
storage: As capacity needs increase, it is simple to
add to the existing storage pool with a SAN. The extra capacity
can easily be distributed to multiple servers.
Ability to share storage: With a
SAN, multiple servers can easily share the same RAID Array, Tape
library, or Optical Jukebox. It is simple to add to the existing
storage pool with a SAN. The extra capacity can easily be distributed
to multiple servers.
Ability to leverage existing expertise:
Many IT administrators are already familiar with the TCP/IP protocol
and related equipment. An iSCSI SAN can easily be implemented
without the need to retrain on the Fibre Channel protocol.
Affordable Disaster Recovery:
Using the iSCSI protocol is a cost effective way to implement
remote mirroring.
Parts of the SAN:
The initiator is a device or piece of software
that 'initiates' communication on an IP SAN. Usually this refers
to an iSCSI host adapter inside of a server or an iSCSI initiator,
which is software that runs on a host to convert an existing Ethernet
adapter (NIC card) to iSCSI. The tradeoff with using a software
initiator with a NIC is that it is considerably less expensive
than an iSCSI host adapter, but it requires more CPU resources.
A dedicated iSCSI host adapter does much of the required processing
in hardware. There are software initiators available for all major
operating systems.
Ethernet cable can either be copper or optical. If using copper, category 6 cable
is recommended but category 5e will also work. Also, limit cable
lengths particularly in electrically - noisy - environments -
optical cable is better in this environment.
Switch: Virtually
any Gigabit Ethernet switch will work well for iSCSI, even inexpensive
ones. However, using switches that support Jumbo frames will increase
performance by allowing you to transfer larger amounts of data
per packet, thus limiting the effects of TCP/IP and iSCSI protocol
overhead. Also, higher end switches provide additional management
capabilities which may be desirable.
Target devices: Since there are no truly native iSCSI devices yet, some kind of
translation device needs to be added to convert iSCSI to the native
protocol of the target device you are connecting. ATTO offers
a line of iSCSI-to-SCSI bridge products that allow you to connect
standard SCSI devices directly to an iSCSI network. The iPBridge
line is easy to use, offers high performance and works with all
types of SCSI devices including: disk drives, tape libraries,
optical jukeboxes, scanners and image setters. Simply connect
the SCSI device to the SCSI port on the iPBridge, connect the
GigE port of the iPBridge to the Ethernet network and map the
SCSI device to an iSCSI Port Address. The SCSI device(s) can now
be accessed on the iSCSIbased SAN.
SAN Management Software: With a SAN, multiple servers now have access to the same storage
LUNs. Data corruption can occur if more than one host is accessing
the same storage LUN because the hosts are not aware of each other's
actions. iSCSI provides for the ability to map LUNs to specific
hosts eliminating the overlap and potential for disaster. There
are environments and workflows that may benefit from multiple
hosts sharing the same LUN. When this is the case:
SAN Management or Volume Management
software is required. Vendors use different approaches to managing
the SAN storage but the basic concept is that software is used
to allow the servers to communicate with each other so that each
is knowledgeable about the data content and access rights for
each piece of shared storage. There are several SAN Management
software packages available, Sanbolic is one of them www.sanbolic.com
If tape drives or libraries are
to be connected to the iSCSI SAN where more than one server will
have the responsibility for managing backups to the same library,
backup software that is SAN aware must be used to manage the sharing
of that library. There are several packages available with this
functionality.
For most other devices management
software is not needed, however, some devices will require that
only one host access the device at one time to avoid errors.
Considerations
If performance is a concern, it is recommended that your iSCSI
SAN be separated from your normal corporate Intranet. This will
prevent your corporate LAN traffic from interfering with the performance
of your iSCSI storage network and vise versa.
Summary
An iSCSI-based IP SAN is an inexpensive and easy alternative to
traditional Fibre Channel SAN technology. Many of the concepts
are the same except that iSCSI uses technology that most IT departments
already have in their possession. The ATTO iPBridge product line
allows you to easily and inexpensively network SCSI devices.
A document written by ATTO Technology
inc.
ATTO Technology, Inc., headquartered
in Amherst, New York, is a global leader of storage connectivity
and infrastructure solutions for data-intensive computing environments.
It is our vision to provide a wide range of endto-end solutions
to help customers better store, manage and deliver their data.
We believe that our company's experience in engineering advanced
technology into real-world product solutions provides customers
a unique competitive advantage.
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