Slashdot Mirror
iSCSI Moves Toward Standard
EyesWideOpen writes "The iSCSI technology, which allows computers to connect to hard drives over a network connection such as a company Ethernet network or the Internet, requires only minor changes before the Internet Engineering Task Force endorses it as a formal version 1.0 standard. A final round of comments has been completed on the technology according to the Storage Networking Industry Association, the subgroup that led the creation of the iSCSI, and as a result companies now can start building iSCSI products."
The difference is very simple:
With a file server (current buzzword is "NAS" for Network-Attached Storage) the server maintains the file system, and multiple clients connect to it to read and write files. It's a shared *file system*.
With a SAN (Storage Area Network) a bunch of raw disks is made available over a network. Currently this is normally Fiber Channel; iSCSI will bring standard Ethernet to SANs, making it much cheaper. No file system is mandated by the SAN; a machine connected to the SAN gets access to one or more raw disks and can use them any way it wants. Typically, the unit of allocation is one disk, though some systems (EMC) allow disks to be subdivided and the sub-disks handed out separately. While the storage pool on the whole is shared, each disk (or sub-disk) is only connected to one machine at a time.
A SAN provides a centrally managed pool of local disk, so you don't have to run around upgrading individual servers. This is a *big* win for large corporations.
For one thing, it's only as reliable as your network. If you have a network problem such as a down switch/hub etc, you lose your disks immediately.
If our Brocade switches go down at work, we lose our Hitachi fiber-channel SAN, too. We also lose our StorageTek 9960. But that's a separate, redundant network, and I'm sure a properly-designed iSCSI network would be separate and redundant as well.
Unlike SCSI and Fibre Channel, you can't boot from an iSCSI volume. This is because your operating system has to be loaded, and your TCP/IP stack initialized, before you can load the iSCSI driver.
Firstly: Why would you want to? Every one of our servers that are attached to the Brocade have their own pair of internal mirrored disks for booting. What's the point of doing it any other way? I guess, if you ever truly needed to boot from an iSCSI device, those issues will be addressed by OS vendors once there's enough uptake for iSCSI.
Most operating systems want to load their storage drivers before they load their networking drivers. Doing it the other way around challenges all sorts of assumptions made by various system software out there. Sounds trivial, but again, we've evaluated it, and the result ain't pretty.
See last point made above.
By putting block level storage on your LAN, you've increased the capacity requirements by several orders of magnitude. To get any reasonable performance you're going to need Gigabit Ethernet everywhere -- and if you're going to make that kind of investment, you might as well be doing Fibre Channel.
Gigabit Ethernet is still much cheaper than FC. I can see the market they're aiming for with iSCSI, can't you?
- A.P.
"Remember when the U.S. had a drug problem, and then we declared a War On Drugs, and now you can't buy drugs anymore?"
For one thing, it's only as reliable as your network. If you have a network problem such as a down switch/hub etc, you lose your disks immediately.
Of course a fiber channel SAN network has exactly the same properties.
Unlike SCSI and Fibre Channel, you can't boot from an iSCSI volume. This is because your operating system has to be loaded, and your TCP/IP stack initialized, before you can load the iSCSI driver. Most operating systems want to load their storage drivers before they load their networking drivers...
This is not true and has nothing to do with iSCSI but rather the iSCSI HBA. An iSCSI HBAs can have their own network stack which not only offloads the networking computes but also configures on its own.
By putting block level storage on your LAN, you've increased the capacity requirements by several orders of magnitude. To get any reasonable performance you're going to need Gigabit Ethernet everywhere -- and if you're going to make that kind of investment, you might as well be doing Fibre Channel.
Look at the figures. A 1Gb fiber channel switch costs roughly twich that of a 1GigE switch. 10GibE switchs are already available, while 10Gb FC still is being debated. The upgrade to GigE will happen naturally on a network. The cost of the switches are ammortized over the network and the switches are cheaper because they don't serve a specialized data center market.
Someone you trust is one of us.