Other iSCSI information sources
15. Where can I find more technical info on iSCSI?
16. Which books about iSCSI and other storage over
IP protocols are available?
17. Is there an e-mail list for iSCSI information?
Did not find an answer you were looking for? -
Ask us an iSCSI question
General iSCSI questions:
Question 1: What
is IP storage?
Answer: IP storage
is a technology that enables block storage transfer over an IP network.
IP storage utilizes existing IP network infrastructure (such as Ethernet),
expertise, and services to build high performance SANs. iSCSI is the leading
protocol standard for IP storage.
Question 2: What
is iSCSI?
Answer: iSCSI
is a protocol that encapsulates SCSI commands in TCP/IP enabling high
performance SANs over standard networking technology, such as Gigabit
Ethernet. The iSCSI standard is being defined by the IETF to insure interoperability.
Here is a more expanded definition from the whatis.com
Question 3: What
is the difference between iSCSI and NFS/CIFS?
Answer: iSCSI
and NFS (Network File System) or CIFS (Common Internet File System - MS
proprietary network filesystem) all allow storage access over IP networking
infrastructure. However, iSCSI enables block storage transfer while NFS
and CIFS transfers files. Ultimately a file is composed at the NFS/CIFS
server device through block level storage access. Block level storage
access offers superior performance for data intensive software applications
and databases.
See the "iSCSI
and NFS performance comparison" whitepaper
Question 4: Why
has TCP/IP not been used for SANs before?
Answer: The
main reason was the absence of a suitable standard protocol along with
an industry-wide organization to facilitate interoperability and promote
the standard.
Question 5: What
is iSCSI good for?
Answer: The
uniqueness of iSCSI is in its ability to transport block-based storage
over any kind of IP network. So naturally, the first use of iSCSI is
remote mirroring, remote backup and similar applications.
Second, as a block based storage protocol, it is superior in speed
to NFS, CIFS and such file-based network storage protocols (see "iSCSI
to NFS performance comparison" whitepaper
), so it can be
used anywhere instead of NFS/CIFS where sharing data between hosts
is not required. For example, as a centralized disk for all workstations.
Such installation will have a benefit of being able to move users between
workstations without moving workstations physically or copying all data
around. Yet, unlike a shared data pool of a central NAS filer, a single
user will not be able to consume all storage resources.
Another use of iSCSI is building of virtual Storage Area Network
without building dedicated Fibre Channel plant. iSCSI can perform all
functions which are currently performed by Fibre Channel, except it runs
on a more affordable physical equipment, like standard Ethernet. It is
also more flexible: it can use any network which supports TCP/IP.
All of those uses and some more are discussed in the
"Data Transport Processor
applications paper"
.
iSCSI Implementation Questions:
Question 6: Do
I need a special HBA to run iSCSI?
Answer: Not
necessarily, but it depends. iSCSI can be used over a standard TCP/IP
link with your existing Ethernet adapter if you have a software iSCSI
driver installed. A dedicated iSCSI HBA can improve performance. Some
operating systems do not have software-only iSCSI drivers available, in
which case, a special iSCSI HBA might be the only choice.
Question 7: Which
software-only drivers are available for iSCSI?
Answer: As of
November, 2003, software drivers are available for MS Windows 2000/NT/XP,
Linux, Solaris and HP-UX. Here are the links to some of those drivers
(in new window):
Question 8: What
hardware iSCSI adapters are available?
Answer: As of
November, 2003, we know of four manufacturers who have released iSCSI
HBA's (in new window):
We are not mentioning so called "TOE NICs", or TCP Offload Engines,
because they are not optimized to be used as a server's storage peripheral
and are generally not supported by major OS manufacturers.
Question 9: Do
I need to build a separate network for iSCSI SAN?
Answer: No,
in most cases you do not. One of the major advantages of iSCSI over Fibre
Channel SANs is that it utilizes existing IP infrastructure. In some cases,
however, it might be desirable to separate storage traffic into a dedicated
network for performance reasons. This is especially true for installations
which do not have a Gigabit Ethernet network installed.
Question 10: Has
the iSCSI standard been finalized yet?
Answer: Yes--In
February 2003 the IESG approved
iSCSI draft 20 (with two brief modifications) as a Proposed Standard.
(For an explanation of the Internet Standards Process and vocabulary,
see
http://www.ietf.org/rfc/rfc2026.txt).
Other specifications related to iSCSI can be
can be found both at the
IETF web site or at
Julian Satran's IPS archive.
Many vendors including TMI have released iSCSI
equipment working flawlessly based on some iSCSI draft revision. Right
now most iSCSI vendors, including TMI, are shipping draft 20 compatible
equipment. All iSCSI equipment is easily upgradeable to the latest standard
through some form of firmware download.
Question 11: How
do I do storage virtualization with iSCSI?
Answer: Storage
virtualization is not done at a protocol level: i.e. it is not dependent
on SCSI, iSCSI or Fibre Channel. It is done at a disk block level. This
means that a virtualization device, like the
Data Transport Processor or FalconStor's
IPStor, can access storage over Fibre Channel as well as iSCSI and regular
SCSI and serve it to computers attached over any of those cables/protocols.
Some storage manufacturers include various levels
of storage virtualization built into the disk arrays. This is so-called
target-based virtualization. In case of TMI's
InfoSlice, an advanced virtualization engine and native iSCSI connectivity
are both available with all models.
Question 12: Which
iSCSI storage devices (targets) are currently available?
Answer: There
are more and more iSCSI devices available on the market. Here are a few
of them (link opens a new window):
Another good source for iSCSI vendor information is
Storagesearch
.
Question 13: What
does a target and initiator mean?
Answer: SCSI
protocol is fundamentally asymmetric in all forms: parallel SCSI, SCSI
over Fibre Channel and iSCSI all have two types of devices which are present
in the connection: initiators and targets.
Initiators are the devices which request, or initiate, any SCSI
communications. They request data writes, reads and any other SCSI operations.
Usually initiator is the HBA in the computer which is using SCSI disks,
tapes and other target devices.
Targets are the devices which perform SCSI commands at a request
from initiators, but never initiate SCSI activity. Examples of SCSI targets
are: disks, tapes, RAID arrays, robotic libraries and many more.
In any SCSI connection there should be at least one initiator and one
target for it to be functional.
Question 14: Can
I boot a diskless machine over iSCSI?
Answer: It is
possible to boot a diskless computer with the help of iSCSI, but it is
a bit more complicated then booting with regular parallel SCSI or Fibre
Channel. The reason it is more complicated is because the computer which
boots needs to have a TCP/IP stack and iSCSI driver configured and working
before it can access iSCSI-based storage. This creates a chicken-and-egg
problem, because most iSCSI client solutions rely on a loaded OS to function.
This problem can be overcome with a
hardware iSCSI HBA, but some software-only solutions are also available:
For Linux OS, there is a
method of mixed-protocol booting, which uses iSCSI for all disk access
once the machine is booted.
There is a protocol for booting over iSCSI being developed with the
help of IETF: see the
"Bootstrapping Clients using the iSCSI Protocol" document on their
web site. Unfortunately, we are not aware of any implementations of this
protocol yet.
Please,
let us
know if you know of a such implementation.
IBM has a proprietary solution called
iBOOT, which allows a computer to boot Windows and Linux. It is a
boot PROM which contains a simple TCP/IP stack and a minimal iSCSI driver.
Recently, Cisco has made available to their customers an
iSCSI boot client, registration and login required.
Other iSCSI information sources:
Question 15: Where
can I find more technical info on iSCSI?
Answer: Here
are some useful links:
Question 16: Which
books about iSCSI and other storage over IP protocols are available?
Answer:
- IP SANs. A Guide to iSCSI, iFCP, and FCIP Protocols for
Storage Area Networks
Tom Clark
Pearson Education, 2002, ISBN: 0-201-75277-8
- Using SANs and NAS
W. Curtis Preston
O'Reilly, 2002, ISBN: 0-596-00153-3
- IP Storage Networking, IBM NAS & iSCSI Solutions
Rowell Hernandez, Chai Cher Kion, Geoff Cole
IBM Redbooks, June 2001, ISBN: 0-7384-2158-8
- Building Storage Networks, 2nd Edition
Marc Farley
Osborne/McGraw-Hill, May, 2001, ISBN: 0-07-213072-5
- iSCSI: The Universal Storage Connection
John L. Hufferd
Addison Wesley Professional; ISBN: 020178419X
Question 17:
Is there an e-mail list for iSCSI information?
Answer: There
is an active
mailing list for iSCSI developers at IETF.
Various iSCSI implementations and/or products also have e-mail lists,
like the
Open source iSCSI driver at sourceforge, but the list is mostly
inactive at this point.
