Serial ATA Implementation

Suggested requirements

What should you be looking for in a SATA disk? That depends on what you want one for. If you are wanting to upgrade your PC hard drive, then you want a big raw SATA disk, say one which holds 3-500GB. If you want to replace tape backups with SATA at your work, then you need a resilient subsystem containing several terabytes, with supporting software. Examples of both these options are given below.

Raw SATA disks

First, a couple of quick tips. It seems that there are problems with the flexibility of SATA cables, and the fact that the cables are unshielded.
To avoid cable failure, do not wrap SATA cables together, and do not put sharp bends in SATA cables.

There are lots of SATA devices on the market. This is a sample to indicate what is available. It is not meant to be an exhaustive list.

The Seagate NL35 is a 500GB SATA device with an 8 or 16MB cache. Seek time is low at 8.5 ms and it appears to be quite quiet. List price is about $400, which prices it at $0.80 / GB

The Maxtor Atlas 15k is actually a 147GB SAS device (see the next page) but is worth mentioning here for comparison. It has a 16MB cache as standard. Selling price is between $640-$975, so best price equates to about $4.35 / GB

The HP PV943A is a 500GB SATA device with a 16 MB buffer. Seek time looks a bit slow at 30ms, and it is a bit pricey at $615.85, or about $1.23 / GB

All these drives run at 7,200 rpm, about half the speed of fibre channel drives.

SATA disk subsystems

There is a large selection of the SATA disk subsystems out there. Prices vary but you could expect to pay between $1,500 and $3,000 per terabyte. A lot of the price is in the controller and software, so if you want full mirroring and snapshot capabilities, expect to pay more. Capacities range from 6TB to 300TB or more. An example is the EonStor A08U-C2410 single RAID controller subsystem from Infotrend. A subsystem will support up to sixteen 750GB SATA/300 drives, delivering a subsystem maximum capacity of 12 TB. It has redundant power supplies and supports a wide variety of RAID configurations. Fully configured 12 Tb price is about € 11,000.

Many suppliers will now let you add SATA devices to high end subsystems, and that lets you do storage tiering 'within the box'. For example, the HP EVA subsystems have this facility. Typical SATA upgrade prices are about $2,000 per TB.

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