Kbase P97610: What is SATA?
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
11/26/2004 |
|
Status: Unverified
GOAL:
What is SATA
GOAL:
What is Serial ATA
FIX:
SATA is a primarily new way of wiring up ATA drives, using a simpler, thinner cable than the older 40 or 80 wire parallel ribbon cables (aka PATA and formerly known as EIDE).
The actual disk drive mechanisms are the same whether serial ATA or parallel ATA.
For the most part, you can expect the same performance and reliability as with PATA drives. Scalability with either type is a function of the quality and features of the disk controllers. 3Ware controllers are excellent in my opinion, not expensive, and /well/ worth the money.
While SATA has the potential to eventually provide higher performance than PATA, that has not really been achieved yet. The cabling is not the biggest determinant of disk performance. And in addition to performance, there are other factors to consider.
There are 4 categories of disk drives, each with a different set of tradeoffs:
Drives for small devices
Things like iPods, cameras, PDA's and the like.
Small physical size and low power consumption are the most important things. Performance does not matter too much. Have to run cold. Capacity is in the 1 to 40 gigabytes range.
Drives for laptop computers
These are typically 4200 or 5400 rpm drives with capacity up to 80 gigabytes. Power consumption and quiet operation are important and performance has to be ok. Heat generation has to be low.
Drives for desktop computers
Typically 7200 rpm ATA drives. They have to be reasonably quiet, give decent performance, and capacity currently ranges from 40 to 400 gigabytes. Duty cycles are 8 hours on, 16 hours off. Drive vendors compete on price and capacity.
Failure rates of inexpensive desktop drives are fairly high, especially if used in continuous operation.
A big disadvantage of ATA drives has been the crappy cabling. Big, flat ribbon cables of very limited length. Controller typically have two channels and you can connect two drives per channel, in a master-slave relationship. The master and slave drives cannot both transfer data at the same time.
SATA improves the cabling problem a bit, but currently each drive has to have its own cable to the disk controller.
Drives for servers
High performance, high reliability are important. Duty cycle is 24 hour per day operation. These drives are often noisy and hot. Highest performance drives are 15,000 rpm scsi 320.
One of the advantages scsi has over ATA is that you can chain up to 15 drives on one scsi controller channel. This makes it a lot simpler to have more than two drives. You can put a bunch of drives in a box and run a single cable from the box to the computer. This is harder to do with ATA. Also, modern scsi controllers can overlap operations on several drives at
the same time and have command queuing which ATA does not yet do.
The capacity of these drives is generally lower than desktop drives, ranging from about 36 to 100 or so gigabytes. The reason is that packing more bits into less space increases the error rate. Small temperature variations and head positioning inaccuracy are likely to cause errors.
Probably the biggest thing affecting drive performance these days is rotational speed. A 15,000 rpm drive can transfer data almost 4 times faster than a 4200 rpm drive.
All that said, 10,000 rpm SATA drives are starting to appear. They perform better than 7200 rpm parallel ATA drives.