By Dave Simpson
— Seagate and Western Digital recently began production shipments of Serial ATA (SATA) drives designed for non-desktop applications. For example, Seagate today began shipments to the channel of its NL35 line of "nearline" SATA drives, which were announced in October 2004.
Examples of nearline applications include disk-to-disk backup/recovery, archiving, and tiered storage (e.g., mixing drives types such as SATA, Fibre Channel, SCSI, etc.).
In terms of reliability, the NL35 SATA drives (which are also available with Fibre Channel interfaces) fall between desktop SATA drives and higher-end drives such as SCSI, Serial Attached SCSI (SAS), and Fibre Channel. For example, the mean time between failure (MTBF) rating for the NL35 SATA drives is one million hours, compared to 700,000 hours for Seagate's desktop SATA drives and 1.4 million hours for Seagate's higher-end disk drives.
In terms of performance, the nearline SATA drives are similar to Seagate's desktop SATA drives. For example, both have a rotation speed of 7,200rpm and a data transfer rate of 1.5Gbps. That compares to 15,000rpm for Seagate's high-end Cheetah Fibre Channel drives.
The main differences between Seagate's desktop Barracuda SATA drives and nearline NL35 SATA drives, other than the MTBF ratings, are that the nearline versions include a reliability feature called Workload Management, as well as a number of features that make the drives easier to integrate in multi-drive arrays, including Error Recovery Control, One-Step Microcode Download, and Write-Same Technology.
Workload Management monitors and manages drive temperature and activity to improve overall reliability. Error Recovery Control improves recovery processes with configurable recovery time and fewer time-out errors. One-Step Microcode Download simplifies multi-drive field upgrades with a single command. And Write-Same technology executes large writes without host interface overhead.
The NL35 SATA drives include 8MB or 16MB of cache and have an average seek time of 8 milliseconds for reads and 9msec for writes.
The NL35 drives are available in 250GB or 400GB capacities. Production shipments of a 500GB version are slated for the fourth quarter. (Hitachi and Maxtor are currently shipping 500GB SATA drives.)
Pricing depends on Seagate's channel partners, but the NL35 SATA drives are expected to cost about 10% more than Seagate's desktop Barracuda SATA drives.
Meanwhile, Western Digital recently began shipping 7,200rpm, 400GB Caviar RE2 (RAID Edition) disk drives that WD rates at an MTBF of 1.2 million hours. The drives are targeted at server and NAS systems.
Western Digital claims the drives can handle high duty cycles (24x7). A Rotary Accelerometer Feed Forward (RAFF) feature maintains drive performance in arrays where rotational vibration might otherwise decrease performance. And a Time Limited Error Recovery (TLER) feature increases reliability by coordinating error handling with RAID controllers.
Caviar RE2 drives include 16MB of cache and an 8.7msec average seek time.
Both the Seagate and Western Digital SATA drives include native command queuing (NCQ) and can be used in SAS enclosures.
At a glance
Seagate's NL35 SATA drives
|Capacity||250GB or 400GB (500GB version due Q4)|
|Interface||1.5Gbps Serial ATA (SATA)|
|MTBF||one million hours|
|Average seek time (read/write)||8/9msec|
|Internal transfer rate, maximum||754Mbps|