SCSI is going serial. Part 1 of this piece looked at the implications of SAS. Part 2 looked at smaller and faster SAS drives. We pick up the story here...
Where iSCSI fits in
Just as storage vendors start to sell SAS and 2.5-inch drives, they're also pitching iSCSI. But iSCSI isn't really a form of SCSI, nor does it have any real relationship with the SCSI technology evolution.
iSCSI is actually an external interface to connect storage systems, similar to FC (Fibre Channel) or Infiniband. An iSCSI connection uses the Ethernet as the data transport and packages the storage management commands for delivery via TCP/IP. But an iSCSI connection works equally with ATA, SCSI, and FC storage systems. (FC is both an external connection technology and a specific drive technology, but similar to iSCSI, it connects any type of drive system.)
That means enterprises should evaluate the merits of iSCSI -- essentially a cheaper SAN connection method with slower performance -- separately from those of SAS and 2.5-inch drives. "The primary advantage is lower cost of connectivity," says Jay Krone, director of Clariion product marketing at EMC.
"There's a school of thinking in the low-end server market that iSCSI would be a cheaper way to do [direct-attached] storage," says Harry Mason, director of industry marketing at LSI Logic. But Mason's not convinced. "SAS took all the wind out of iSCSI's sails in that kind of implementation because it gives all the predictability and bandwidth without having to build a new environment." Mason, citing offerings from companies such as LeftHand Networks and EqualLogic, does see iSCSI as an appropriate SAN alternative for low-performance environments such as small businesses and for linking isolated SANs.
SAS on tape offers high-end backup for less
SCSI is used in tape drives, not just disk drives, but there's been little public attention paid to how SAS would be deployed in tape libraries. Seagate's Franco Castaldini notes that no tape vendors have yet attended the SCSI Trade Association's "plugfests" where vendors test SAS products, for example.
Optimus Solutions consultant Greg Hartzog believes that SAS could be a great benefit to tape libraries because of the increased cable length and the smaller, more flexible cable size. He says his customers like the idea of external but direct attached tape libraries for departmental and other local backup. LSI Logic's Harry Mason agrees, saying that tape libraries have not fit well in most enterprises outside of FC (Fibre Channel) connections because tape libraries don't typically connect to a backplane as disk drives do but instead connect via cables.
But FC tape-drive adapters cost about $US1000, Hartzog notes, making IT think twice before deploying them. "SAS tape should easily compete on price," he says.
Mason says he's seen "a lot of interest from the tape providers in SAS designs". One reason is that the SCSI protocols have "always been a fairly good portal to the robotics of the tape drive", says Kevin Schoonover, director of engineering at distributor Arrow Enterprise Storage. With its SCSI basis and better cabling option, tape providers can now consider SAS instead of the pricier FC, gaining the benefits of a cabled connection without having to migrate to a different command set, Schoonover says.