What's in a name? SATA II Misconceptions
by Kristopher Kubicki on June 20, 2005 3:12 AM EST- Posted in
- Storage
Recently Purav and I had the opportunity to work with some retail "SATA II" drives as part of some upcoming articles. Even though we have known about SATA II for well over a year now, seeing retail drives has been really refreshing as Western Digital, Samsung and Hitachi all have units available [RTPE: "SATA II"]. However, the real surprise to us came when the majority of SATA II drives available right now are not capable of 3.0Gbps transfer speeds and others don't claim support for features we almost take for granted; like NCQ. The original SATA standard - usually referred to as SATA, U150, SATA150, or SATA I - gave us a peak transfer rate from the HDD interface to the system bus of about 1.5Gbps. Many believe that if SATA I drives have transfer rates of 1.5Gbps, then 3.0Gbps rates must be held by drives which have SATA II in their names. This is definitely not the case according to the SATA organization:
"The first step toward a better understanding of SATA is to know that SATA II is not the brand name for SATA's 3Gb/s data transfer rate, but the name of the organization formed to author the SATA specifications. The group has since changed names, to the Serial ATA International Organization, or SATA-IO." - SATA-IO, http://www.sata-io.org
The three main misconceptions are that:
- "SATA II" has now been renamed to SATA-IO
- SATA-IO must support 3Gbps transfers
- SATA-IO must support features like NCQ and Hot Plug
The SATA-IO, or SATA International Organization, specifies that the SATA standard has the potential to top 6Gbps transfer rates; four times what the majority of drives currently offer. While it is probably questionable if 3Gbps transfer rates are even obtainable outside all but the most intensive SATA RAID scenarios, the fact remains that "SATA II" - the name - has absolutely nothing to do with data rates. Also recall that even though a SATA device might claim 3Gbps transfer rates, 20% of the bandwidth is dedicated for parity in the encoding scheme of the bus - which is why we claim effective thoroughput of 300MBps as opposed to 375MBps.
SATA-IO claims we should identify SATA products in much the same manner we identify CPUs; by distinguishing the speed and feature set in the product description. From the SATA-IO website again:
Just because the SATA-IO committee identifies capabilities like NCQ and Hot Plug, they are not required by any standard; however, any device identified as "SATA II" or "SATA-IO" (also mentioned as "SATA Gen 2" in some documents) are backward compatible with SATA I technologies. Frame Information Structure (FIS) based switching supposedly enables smaller RAID stripes to obtain near 2Gbps transfer rates, something not yet capable on existing U150 SATA devices. Getting the word out to IT managers and administrators that "SATA II" devices are not always what they seem now becomes a large challenge for the SATA organization.
Since there is a clear possibility that manufacturers might offer non-NCQ "SATA II" hard drives - let this be a word of warning. Hopefully the market will load up all of the capabilities of SATA whenever a new device comes out, but we get the distinct feeling that purchasing a new hard drive or RAID controller will become a more researched purchase than it has in the past.
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braytonak - Wednesday, July 27, 2005 - link
This is just so stupid. We supposedly have this international organization to come up with what the stanard should be. But, they don't have the common sense to be the ones that decide how it's labeled on packages? That's brilliant. Now the marketing dip-shits at WD, Maxtor, Seagate, Hitachi,etc, will have free reign over what to call this stuff.It's on the path to being as totally logical and easy to figure out as SCSI. And that's just scsi!
piasabird - Saturday, July 16, 2005 - link
I realize a Cache might speed up a hard drive a little, but putting that aside, a hard drive has to be able to read the data before it can transmit it over the SATA/SATAII I/O interface. I dont think even with 2 hard drives in raid you can exceed the ATA133 I/O transfer rate.I think this is much ado about nothing. The transfer speed is faster than the hard drive can physically retrieve the data without a valid reason to be. What we need is better hard drives not a faster transfer rate. I have thought we need to take the raid concept and build that into a single hard drive at the hardware level. If a hard drive can have 3 metal platters, why cant it raid itself?
rprice999 - Tuesday, July 5, 2005 - link
This is all a crock anyway, I have never even gotten over 75megs/second transfer rate on my SATA Raid 0 setup.NCQ will be a help, but increasing throughput to 3gbs when 1.5 is not even close to attainable in a real world setting is just a waste.
Cullinaire - Thursday, June 23, 2005 - link
SATA 360 coming soonJarredWalton - Tuesday, June 21, 2005 - link
12 - The point of the article is that just because a drive says it is "SATA II", that doesn't mean it will have NCQ or hot plugging support (among other things). I know Kris and I had assumed that "SATA II" at the very least included these two features, whereas on "SATA I" they were optional. The only thing SATA II seems to guarantee right now is 300 MBps of theoretical bandwidth (theoretical meaning no drives can really make use of that right now).Do the WD SATA2 drives support NCQ? I don't know. Hopefully we can find out soon. :)
evenglow - Tuesday, June 21, 2005 - link
I seriously don't understand this article. The last time I looked WD did offer SATA2 hard drives at 3Gb/s. I know that Newegg for awhile was advertiseing Seagate drives as SATA2 but I just looked and they stopped doing that. Now there is Serial Attached SCSI drives out.n00btoo - Tuesday, June 21, 2005 - link
This part of the article is confusing:>The three main misconceptions are that:
>- SATA II" has now been renamed to SATA-IO
Wasn't this just mentioned in a previous quote:
"...SATA II is not the brand name for SATA's 3Gb/s data transfer rate, but the name of the organization formed to author the SATA specifications. The group has since changed names, to the Serial ATA International Organization, or SATA-IO"?
ceefka - Tuesday, June 21, 2005 - link
I feel a little lost here. This is actually sloppy work by these SATA-fellows.I'm with #4: let's have a SATA roundup where HDDs carrying the SATA-II label can proof what they are really about. We should also include mobo support. To what extend do popular mobos with "SATA-II support" really support all the goodies?
JarredWalton - Tuesday, June 21, 2005 - link
This is really like the days of "ATA-100" and "ATA-133" - the latter of which never was an official ATA spec. What will "SATA II" actually add relative to SATA? Higher burst transfer rates, which will mean very little. With 16MB of cache, it takes less than .1 seconds to empty the entire HDD buffer, and we can now get that down to .05 seconds! Woohoo!Pariah - Monday, June 20, 2005 - link
"what would a SATA II drive that just meets the base requirements have over a SATA I drive"There is no 2nd generation spec, so no one knows or can tell you. The features you listed were all expected to be in the spec so it looks like everyone jumped the gun and just implemented the features and slapped a SATA II name on it, since that what it used to be called. The SATA II committed broke up, and then reformed as SATA-IO, but it's too late in the game to try and change the name now, everyone is familiar with SATA II, so whether they like it or not, the features we have become familiar with being attached to SATA II is what it is going to be even if a real 2nd generation spec is released that is different.