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."

Comments

iSCSI not ready for prime time

[IGnatius T Foobar]

I work at a mid size hosting facility, and we've done quite a bit of experimentation with iSCSI. In my opition it's not ready yet. Either that or it's just a bad idea, full stop.

We do quite a bit with our SAN -- there are a coupla IBM 2105 ESS ("Shark") boxen in the back of the data center with many terabytes of disk online. It's all about Fibre Channel. At least as fast as SCSI, effectively faster when you have all sorts of cache running on the storage side, and you have the flexibility to define exactly how much disk goes to what server, and you can add more dynamically without a power down, etc.

Unfortunately, Fibre Channel is expensive. It requires expensive host bus adapters and even more expensive switches. And of course it runs over fiber optic cable, which isn't exactly penny kit. So the industry decided to try running it over Ethernet.

Now there are iSCSI-to-Fibre gateways, such as Cisco's 5420 Storage Router (which we've evaluated), but there are just problems in general with running block level storage over a TCP/IP network...

• 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.
• 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. 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.
• 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.

That's why our iSCSI stuff is just sitting around doing nothing right now.

The only place I can see iSCSI being used at this time is for really temporary quick-and-dirty setups, such as a programmer needing another 100 GB online for a one-week project. But even then, NAS seems like a better idea.

Re:iSCSI not ready for prime time

[Wakko Warner]

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.

Re:iSCSI not ready for prime time

[selectspec]

FUD alert:
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.

Re:hum..

[SQL Error]

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.

iSCSI nearly ready for prime time

[crow]

We're starting to see PCs ship with 10/100/Gig ethernet standard. Within a year or two, it won't be unreasonable to run GigE to every desktop in the building.

Now consider what iSCSI offers the system admins. You can use the network boot option on the desktop systems and run them diskless. This means you can centralize your storage. No longer to you face the daily panic of a user desperate to recover a file they only saved on their local hard drive. If someone is having trouble with their system, you just give them a fresh boot image; if the problem persists, it's hardware. If I were a sysadmin, I would be pushing hard for iSCSI.

And from the technology standpoint of iSCSI vs. Fibre Channel, I expect that ethernet speeds will outpace Fibre Channel speeds; it's a larger market, so the R&D investment will go there first.

[Disclaimer: I work for a data storage company, but everything stated here is based on general observations and opinions, not insider information.]

anytime you read IETF is about ready to approve..

[keithmoore]

Anytime you read that IETF is about ready to approve something as a standard, take it with a grain of salt unless it comes from the IETF chair or the area director responsible for that group. Such statements are usually propaganda from people who are trying to encourage premature adoption, or at best they are wishful thinking. It's not unusual for working groups to produce drafts which they think are ready for approval, but which actually contain serious technical problems that need to be resolved. Fixing those problems can require months or even years.

In particular, the fact that The Storage Networking Industry Association has completed its comments on the draft doesn't have any bearing whatsoever on IETF standardization.

Someone mentioned the security issue. I haven't followed the iSCSI discussions but security is definitely an issue that was identified before the group was formed, and one which is particularly difficult to solve for iSCSI because of performance concerns. I'll be interested to see how they've addressed it. I'd consider it extremely unlikely for IETF approve the standard without due consideration of security. And saying "it's going to be behind a firewall, so it doesn't have to be secure" has traditionally not been considered sufficient.

(FWIW, I'm a former IETF area director)