• United States

The disks spin on

Jul 03, 20033 mins
Data Center

* Catching up with disk drives: SCSI and ATA

What is happening with disk drives these days?  As it turns out, quite a lot.

SCSI, which dates back to the late 1980s, has been the standard for direct attach drives and for many RAID systems for quite a while. (In case you have ever wondered about it, “SCSI” stands for “small computer system interface,” although it clearly is in use in very large systems today). Fibre Channel, which started to be used in the late 1990s, is what most of us now expect to see on storage-area networks. When it comes to enterprise environments, these two protocols have ruled the roost for a decade and a half. 

Until recently, ATA (also called IDE) had almost no play in enterprise data centers.  ATA drives were built for a commodity market, where cheaper is always better.  Cost-reduced drives were achieved through building them from cheaper parts and by selling them by the boxcar load. Thus, these devices were not competitive in terms of either performance or duty cycle.  As a result, ATA drives appeared in a few low-end JBOD devices that went into small and mid-sized businesses. But by and large, ATA technology was considered to be fine for the desktop but not robust enough for the computer room.

Much has changed, of course, as companies have realized that all data does not have to be treated the same way, and that some of it can be assigned to lower performance, lower availability storage.

These days many vendors offer enterprise customers an ATA option, and some (EMC’s recent Clariion offering is a good example – see story link below) have even created an architecture that permits users to combine ATA and Fibre Channel devices within the same cabinet.  Implicit in this approach is an understanding that users may want flexible storage (“flexible” here refers to both performance and availability).  These ATA-based devices can be used for both primary and near-line storage, or can be used as staging areas in a disk-to-disk-tape backup strategy.

ATA has always been a parallel technology, as has SCSI.  But both technologies have come up against performance, distance and manageability limitations inherent in their parallel design and both are in the process of changing to serial implementations.  Serial ATA is already a product (from Maxtor, Seagate and Western Digital), but serial SCSI is just “going into committee” and has a way to go before it becomes an industry-approved standard.

SCSI and ATA are usually looked at separately. Next time however, we will consider the potential impact of these two serial technologies on one another, and begin to make some inferences about what may be in store for us when we next start to reexamine our investments in storage devices.