The Value and Position of iSCSI
To the Reader
This chapter will take you through the different environments in which network-connected storage may be appropriate. Because market planners and engineers may have different views on the potential market for iSCSI products, we will discuss what the market looks like, in hopes of bridging the divergent views.
A taxonomy of the various environments is listed, and each area's potential relative to iSCSI is explained. This entire chapter is therefore recommended reading for marketers and hardware and software engineers.
Small installations are called SoHo (Small office, Home office) environments. In such environments customers will have one or more desktop systems, which they are tired of constantly opening up to install storage devices. They want easy interconnects that permit them to operate with external storage as fast as they can operate with internal storage.
The Home Office
Generally the home office will have computers that are connected on small locally attached Ethernet 100Mb/s links. These systems typically have more processing power than they have storage access capability. These installations will find value in placing their storage in a central location, dynamically adding it to their personal computer systems with a simple plug-and-play configuration, thereby obtaining additional storage without having to open up their systems.
The home office environment can use standard, low-cost, off-the-shelf networking components. The switches are readily available, and the desktop and laptop processors usually have more processing power than is needed for the types of work they do. These home office systems usually come with Ethernet connections and do not need any special adapter cards. The only things they need are iSCSI software drivers and the low-cost IP storage devices that iSCSI will permit.
For the home office, vendors are bringing to market a simple disk controller that can attach from one to four (or more) low-cost ATA desktop-class drives. These controllers and drives will be purchased at local computer superstores for very low prices. Moreover, the customer will be able to buy one or two drives initially with the basic controller and then add drives whenever they wish.
Customers can now purchase 10/100/1000 Ethernet cards that can operate over the inexpensive Cat. 5 Ethernet cable already installed for their existing 10/100Mb/s network.
Prices for 10/100/1000 Ethernet NICs and switches are dropping rapidly. In early 2002, 10/100/1000 Ethernet NICs cost $60. The then current 10/100 Ethernet NICs cost only $30, down from $60 just a year previously. It seems reasonable to assume that the 10/100/1000 Ethernet NIC will soon be the default in most desktop systems, which means that the home office will have gigabit capability and processors fast enough to at least utilize 300 Mb/s. This will give desktop home office systems as much storage access as they can use.
Usually home offices obtain all their software either from the OS that came with the unit or from a local computer store. There is almost no software in this environment that knows how to work with shared files, and it is very rare to see a file server in this environment.
Home offices use peer-to-peer file-sharing functions that come with the OS to permit one user to operate on a file created by another (serial sharing). However, the storage is considered to belong to the system to which it is attached. As a rule, when one home system runs out of space, owners do not use the space on another system but instead upgrade the storage on each system independently as needed. iSCSI will permit home office users to set up their own external storage pool connected via a LAN. The owner will then assign new logical or physical hard disk drives (HDDs) to each host system without needing to open or replace them. (See Figure 21.) We have been talking as if the home office had more than one host system. This is because owners of home offices tend to keep their old systems, which have old data and applications that still work. Also, the home/family use dynamicthe multiple computer familyis often at work. Many times there are two, three, or more computers in the same familyone for each adult and one for the childrenbut only one person is responsible for maintaining them all. In these environments a shared pool of storage is valuable for ease of both access and administration.
Figure 21 The home office and iSCSI.
Even though multiple-system households are common, it is also true that home offices may have only a single desktop or laptop system. But even in single-system environments, the owner will want to have storage attached externally to avoid the problems of opening the system and adding new HDDs. Unlike other environments, these systems are often updated to add processing power not only for business but also for game playing. Whatever the reason, they will find iSCSI very useful in avoiding having to transfer all their key files from old systems to new systems, since the storage is all external. (And yes, iSCSI has boot capability.) It has been pointed out that even in a home office, doctors, lawyers, and others would love to have their data placed on small, inexpensive RAIDs (redundant arrays of independent disks) because of their reliability. And iSCSI provides even this "upscale" home office the most appropriate, flex-ible, and inexpensive interconnect for that need.
The Home Office and Serial ATA Drives
At least one individual has made the claim that iSCSI's real competition is the new serial ATA (S-ATA)a cabling protocol that travels from the controller chips on the motherboard directly to the HDD. This is not a true consideration today, since the S-ATA is currently 1 meter in length and has no sharing capability. Therefore, it is unlikely that it will be used for a cabling interface that hangs out of a home PC for a general storage interconnect. There is a proposal for increasing the length, but this is for rack mount versions and it is not clear if that will ever affect the desktop or home market. Further, the S-ATA specification has not yet defined a technique for permitting the same storage device to be attached to more than one system at household distances. Within the iSCSI target, however, one may find iSCSI coming into a small box and then interconnecting to the ATA disks with S-ATA cables. (See Figure 22.)
Figure 22 Attached serial ATA storage controllers.