Exploitation of IP networks expands SAN possibilities; performance vs. Fibre Channel must be weighed.The release of the iSCSI specification is just around the corner, and, based on eWeek Labs tests of iSCSI-based products and analysis of the evolving specification, iSCSI will offer organizations an inexpensive, effective means to a SAN end.
iSCSI is an IP-based protocol that enables the block-level transfer of data over a network. From a servers perspective, iSCSI essentially allows standard Fast Ethernet and Gigabit Ethernet network cards to function like storage area network controllers. iSCSI will also allow shared storage solutions such as tape drives and RAID units to be shared over IP.
Although the iSCSI specification is still in development, products that take advantage of this new storage protocol are already on the market. In fact, they have been kicking around in testing labs and early-adopter sites for close to a year now.
The most compelling use for iSCSI is for SAN expansion to low-end and midrange servers. Using storage routers such as Cisco Systems Inc.s Cisco SN 5428 (click here to see a review of the router), IT managers will be able to hook more servers into their storage networks and take advantage of the IP networks they already have in place. This will save organizations tens of thousands of dollars over Fibre Channel HBAs (host bus adapters), which typically cost from $1,000 to $1,500 each.
In addition, because iSCSI runs on standard IP networks, there is no need to implement Fibre Channel switches throughout a corporation. IT administrators can instead make use of Gigabit Ethernet network adapters, which cost a fraction of the price of Fibre Channel HBAs and are now built into many new servers motherboards.
iSCSI also cuts costs in less tangible ways. The number of people skilled in IP networking is still far higher than those with Fibre Channel networking expertise, and it is unlikely that an influx of Fibre Channel know-how will flood the market any time soon. Organizations can thus tap the expertise that already exists in-house.
Manageability is another area where iSCSI can cut costs. While security and QOS (quality-of-service) technologies are almost foreign concepts in the Fibre Channel world, they already exist in the IP world and might improve the manageability of SANs using iSCSI. Indeed, based on what we have seen from the Internet Engineering Task Force IP storage group, the iSCSI management standards are nearly complete and so will be available to organizations making the move to iSCSI.
iSCSI will also serve as a capable means for enabling long-range data mirroring for disaster recovery, allowing servers in one data center to back up data to remote tape drives. With the abundance of IP networks available, IT managers will be able to use virtual private networks to create secure tunnels between sites to transfer data over the Internet, providing an economical alternative to running leased lines from site to site. (Click here to see iSCSI product forecst.)
Performance Concerns
The most glaring weakness of iSCSI when compared with Fibre Channel is performance. Any way you look at it, 2G-bps Fibre Channel networks are going to be faster than Gigabit Ethernet solutions.
However, as we have seen in our tests of iSCSI-based products from Nishan Systems Inc. (iSCSI/Fibre Channel switch), Alacritech Inc. (HBA) and Cisco (router), iSCSIs performance—while inferior to Fibre Channel in raw speed benchmarks—is still very usable in the real world. iSCSI should work fine for workgroup-class e-mail servers, file servers and even some lightly accessed database servers. And performance may be a moot comparison point as 10 Gigabit Ethernet becomes available.
However, IT managers shouldnt use iSCSI over Fibre Channel in environments that require high throughput or that need to process large amounts of transactions per second (such as high-end databases).
TCP/IP-offloaded adapters from vendors including Alacritech and Emulex Corp. should also help boost the performance of iSCSI. More importantly, they should lower the amount of CPU resources eaten up by networking tasks, freeing up precious cycles for applications.
In addition, as storage management tools get more intelligent, iSCSI may allow IT managers to create truly distributed storage networks, where storage space is transparent to users and servers, and volume management and QOS are automated to ensure constant performance.
Senior Analyst Henry Baltazar can be reached at henry_baltazar@ziffdavis.com.
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