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?

It would be great to have your feedback on this topic
so leave a comment or two!