iSCSI anyone?

iSCSI is a technology which seems to have been cropping up a
lot recently—while visiting a conference on the topic of data protection and
compliance, iSCSI was being pushed as ‘the next big thing’ in storage.

So what is iSCSI? iSCSI is a protocol defined by the
Internet Engineering Task Force (IETF) which enables SCSI commands to be
encapsulated in TCP/IP traffic, thus allowing access to remote storage over low
cost IP networks.

What advantages would using an iSCSI Storage Area Network
(SAN) give to your organisation over using Direct Attached Storage (DAS) or a
Fibre Channel SAN?

iSCSI
is cost effective, allowing use of low cost Ethernet rather than expensive
Fibre architecture.
Traditionally
expensive SCSI controllers and SCSI disks no longer need to be used in
each server, reducing overall cost.
Many
iSCSI arrays enable the use of cheaper SATA disks without losing hardware
RAID functionality.
The
iSCSI storage protocol is endorsed by Microsoft, IBM and Cisco, therefore
it is an industry standard.
Administrative/Maintenance
costs are reduced.
Increased
utilisation of storage resources.
Expansion
of storage space without downtime.
Easy
server upgrades without the need for data migration.
Improved
data backup/redundancy.
You’ll notice that I mentioned reduced administrative costs;
I was very interested to find this document prepared
by Adaptec on the cost advantages of iSCSI SAN over DAS or Fibre Channel
SAN—most notably the Total Cost of Ownership analysis, stating that one
administrator can manage 980GB of DAS storage, whereas the same administrator
could manage 4800GB of SAN storage. Quite an increase!

Isn’t there going to be a bandwidth issue with all of this
data flying around? Well, this is a question I had but found the answers in
this very informative ‘iSCSI
Technology Brief’ from Westek UK. Direct
attached U320 SCSI gives a theoretical data transfer rate of 320Mbytes/s; on a
standard Gigabit network, iSCSI will provide around 120Mbytes/s; and Fibre
Channel provides up to 200Mbytes/s, but at considerable cost. 120Mbytes/s is
probably fast enough for all but the most demanding applications. All
connectivity between the iSCSI storage and your servers would be on a dedicated
Ethernet network, therefore not interfering with your standard network traffic
(and vice versa). If this isn’t enough, 10Gbit copper Ethernet is now pushing
its way on to the market and costs are falling—this would give a possible
1Gbyte/s of throughput!

Most iSCSI devices I have seen give the ability to take
‘snapshots;’ this snapshot will only save changes made to the file system since
the previous snapshot—meaning you won’t need to put aside huge amounts of
storage while maintaining the possibility of rolling back to a previous state
after disaster (data corruption/deletion). Snapshots only take a few seconds to
perform (compared to hours for a traditional image to be created) and can be
scheduled for regular, automatic creation.

I have recently been asked to look at consolidating our
storage, and iSCSI looks like an innovative, well supported, and cost effective
way of doing this. The Power iSCSI range from Westek UK looks very promising
with the option of 10GBit connectivity, Hardware RAID6 (offsetting reliability
concerns due to SATA disks), plus an option of real-time replication and
fail-over between two units.

Have you deployed iSCSI-based SAN within your organisation?
Do you know of any other iSCSI appliance providers offering innovative
features? Maybe you decided to go with Fibre Channel instead? What kind of data
transfer rates do you require for your storage? Do you feel modern SATA disks
provide good enough performance and reliability or are expensive SCSI disks
still worth the premium?