New Seagate Momentus XT 750GB w/ 8GB NAND (and more)

No one has ever stated that it is a sophisticated or overly efficient cache, just an extremely rudimentary one with Seagate proprietary algorithms.....................

Edit; I would also imagine if need be block data written to NAND could also be read from NAND as well. The advantage of block data to NAND is no rotational or seek latencies in reading or writing.................

 

Good luck to you.

Then it is the equivalent of having a Small SSD Buffer. More than likely, your system already has Write Buffers between the BUS and the HDD. You can add something in between to HELP, but the eventual BOTTLENECK of writing to the HDD remains with a BUFFER. The OBJECTIVE of not hitting the HDD is lost. The BOTTLENECK is not eliminated, at most it is DELAYED and even if/ when that is done the SLOW DOWN will still occur.

On the other hand, due to what a CACHE does, it AVOIDs hitting the HDD completely. That's why there is a CACHE Hit/Miss ratio. The more number of times that a CACHE.. already has what is NEEDED, the HDD seek is eliminated.

In a write buffer no matter what you do, the HDD has to be sough to commit the data.

This is the same issue that happens when you windows XP copy a file to a USB HDD, I've had times where the data was not committed to the external HDD and it remained in the WRITE BUFFER.. and then some errors / some data was not copied to disk correctly.

Now the beautiful question - Why cant this be fixed to work like a CACHE?
e.g. Sample Data Points
HDD (500 GB .. Many data points e.g. 1000,000,000,000 + ) > HDD Cache (Lesser e.g. 16/32/ 64 MB) > SSD Cache (Lesser) - Many to Less mapping done by the Caching Logic - Reducing and Filtering down by some Logic

Write Buffer (Memory or SSD/ NAND) > HDD - One to One mapping - No reduction Logic possible - Only fast buffer - STAGING - Staging could be in DRAM or SSD NAND. Hardly matters because the performance hit or the POINT OF FAILURE or WEAKEST LINK / SLOWEST is the HDD.

You may delay the HDD hit, but you cant eliminate it. There i comes another issue, what you assumed was written to Disk may not have persisted if something remained in the BUFFER and did not commit - lets say when your machine crashed or power went out.

RELIABILITY & CONSISTENCY is hard to achieve. Doesnt mean there cant be designs that help - Queue / Buffer management priorities based on HDD Head positions on Disk Cylinders.

Again I say, you have a choice - LEARN or ... be in IGNORANCE = BLISS

Enjoy. I am done trying to help educate those who are set on in imaginary thing, when the fundamentals are easily understood. No wonder so many MYTHS in the Computing World still prevail.

 

Your problem is between designation of a system and a devices on board cache. You are correct this is a hardware buffer/cache not a true system cache stopping bus commitment. The idea is to speed up bus commitments by placing a cache on the device hardware.

The problem is these are SATA drives with the controllers on the drives themselves. You can not make them a true system cache as data has to be committed over the bus and flushed to the device. This is the same reason a true SATA III SSD as a swap file is still infinitely inferior to true ram.

Also with Seagates algorithm the NAND data pushes all cached blocks of data before the HDD media. This is done by the XT's internal controller. (How I understand it) With the new write the available blocks are supposedly mimicked by NAND so when a write command come in it goes to NAND eliminating rotational and seek latencies. At idles times the data is supposed to commit to magnetic media, but we will see how well this works.

IMHO learning is a great policy but teaching is better...................

 

Seagate has a white paper on the XT drives. When the drive gets it write..it's very fast. If it's a miss then I see a hit in performance. Still saving for that 500G SSD, 5 year warranty for $150. My old 500XT is still kicking @$95. Not sure if the 750XT's warrant the expense but may try one when price comes way down.

 

Good write up I like it.

Still does not ELIMINATE HDD Rotational Seek - That is by design - DELAYS it and possibly by intelligent algorithm, commits some smart way.

That is still a SSD NAND WRITE BUFFER Not an SSD READ CACHE

 

crashy,

In general terms, this is not always true. It depends on the implementation of the cache, as cached data can be written to if so designed. Write does not necessarily flush it (invalidate it) from the cache. Cache behavior depends on your cache write-policy to determine what happens to that updated cached piece of datum. There are write-through policies in which the cache and the data backing that up are are both updated and there are write-back policies in which the cached data is updated, but the backing store is not updated until a later time.

If you have Win XP or higher, you can see this from Device manager. Open up the properties of a disk, on the "Policies" tab you can control the write-caching policy on your hard drive. You can configure Windows to use a buffer as a write cache between disk and the system.

But then again, this is a system disk cache maintained by Windows. Not a piece of hardware found on a disk drive.

Note, I believe you may be getting at disk buffering. Agreed, disk buffering is not a cache. In fact, the XT has a 32MiB buffer for queuing items for platter based disk writes and reads. However, this is not how the XT's SSD portion works. It has a component called "Adaptive Memory", which is a custom piece which does block level duplication between disk and SSD. When a READ request comes it, it can act like a cache and provide the data out of the NAND cells rather than get them from disk. However, (especially in Gen 2), many multiple reads do not necessarily mark a block as something to be removed from the NAND portion, and those blocks can remain there for future READ requests. This is helpful for READ requests during a boot process as you don't want those NAND cells invalidated over a long period of use.

More general type info at :
http://en.wikipedia.org/wiki/Disk_buffer
http://en.wikipedia.org/wiki/Cache_(computing)

 

What is the model numbers for the "Seagate Desktop SSHD", can't find them, could only find laptop ones..

thanks

 

First Gen XTs Seagate ST95005620AS (500GB)

Second Gen XTs Seagate ST750LX003 (750GB) / ST500LX003 (500GB)

Third Gen - ???

I'm a bit confused on the third gen product. For example, I can buy a STBD750100 750GB, which is a 7200RPM, but I've seen other reports the 3rd Gen are 5400 RPM based drives. Perhaps the drive speed is based on drive size?

 

Is there any way to disable the 512e emulation and use native 4k? thanks

 

All of those links refer to the ram buffer included on a standard HDD. We are talking the NAND cache of the XT drives. The proprietary algorithm is to try ind increase hit rates to the NAND over the mechanical portion. Now this does work better for some than others according to usage but that is not the point...............

 

The first link is, the second is not, but rather to the general notion of a "cache" within computing. Trying to push thru to crashy the difference between a buffer and caching. The XTs NAND portion within the drive -> operates as a READ cache of the data also existing on the drive. There's no buffering (read-ahead) stuff within the drive itself. Buffering "may" take place on the 32MB disk buffer if not found in the XTs NAND cells otherwise buffering would take place at the OS or higher level up the hardware/software stack.

 

And as per your second link "While the hard drive's hardware disk buffer is sometimes misleadingly referred to as "disk cache", its main functions are write sequencing and read prefetching. Repeated cache hits are relatively rare, due to the small size of the buffer in comparison to the drive's capacity. However, high-end disk controllers often have their own on-board cache of hard disk data blocks."

This is what the XT tends to mimic, a higher end controller with its own on board cache made of NAND................

 

Agreed. As long as we also agree the data blocks found in the NAND are not there due to "locality" or "prefetching", but rather on what the drive's controller determines is the most commonly accessed LBAs through Adaptive Memory Technology.

Note, my main concern on these posts was the incorrect use of the term "buffering" in regards to how the SSD portion is used in tandem with Adaptive Memory Technology on the Momentus XT.

 

So the second generation 750 hasn't gotten a firmware update to bring it in line with the third generation, has it? They said it would be getting a write caching firmware update at the beginning of its life, but they appear to be keeping that exclusive to the third gen now.

 

Ditto this question. They said they'd enable write caching/buffering (whatever) on the 2nd gens.

 

I can never get a solid answer out of them, honestly I think they're hoping people will forget.

When the first round of reviews for the second gen XT came out, a lot of reviewers said Seagate would be releasing such a firmware update late last year. Now, since the third generation is completely underwhelming apart from price reduction, I think they're changing their plan and saving it just for that to give it something special.

Who knows, maybe it just needs more time to port over, but that doesn't seem likely as the drives are so similar minus spindle speed.

It would be pretty crappy of them to deliberately drop this promised future feature just to make the third gen look better.

 

They may be a bit weasily about this statement. I don't recall seeing anything "officially" stated by them they would do this, but only thru 3rd party channels (like the 2nd Gen review). And I haven't seen anything in the 8+ months past their original date.

My guess is they're hoping ppl forget about it. Quite a shame that it appears as this is where it appears this is heading.

 

Hey:

I need a new HDD and was looking at the Seagate Momentus XT SS-HDD 750 GB for replacement.

I was also looking at the WD7500BPKT, a 7200 RPM, SATA 2.5" 750 GB HDD, with a 5 year warranty. The WD drive from what I read is comparable in speed to the Seagate hybrid according to Amazon reviews and other tests reviews. The price on this drive is about $41 cheaper than the Seagate HDD.

There are quite a few HDD's that would work for my Acer Vista laptop, so any suggestions/input welcomed. I am looking to upgrade my OS and memory also.

Any input appreciated, thanks.

 

Most of the benefit you'll see with the Seagate Momentus XT hybrid drive is faster boot times and faster load times on games/applications you use a lot, usually it takes about 3-4 loads to cache reads.

I'm currenty using the 750GB version in my Asus K55N, other than the faster loading times I mentioned above, the write speeds are about the same as normal 7200rpm drives in that capacity range, so a little over 100MB/s, anything that's not cached for reads will also get around 100MB/s.

Which drive you get depends on how much speed and capacity you want, SSDs provide very fast speeds overall but are pricy and lower capacity, regular hard drives are inexpensive and provide a ton of capacity. If you don't mind spending a bit extra and mostly want faster boot times, the Momentus XT is a good choice, if you don't care about boot times or you want faster loads across the board, you will probably want to look at something else.

 

Thanks for the reply. I don't do gaming, but would like an improvement in start up and load times. It takes about 1-1/2 to 2 minutes to load a Firefox page on start up. I don't need much storage space, as I don't do photo editing or anything major. Do word processor stuff, personal pics, basic e-mail and Internet stuff.

But I like the dual purpose of the hybrid drive, a little bit of SSD, flash, and HDD space. More bucks than regular HDD, but think its worth a go. Seems the 750 GB drive has better performance based on the reviews I've read. Don't know if there is anything currently comparable/available price/performance wise? That was part of my inquiry?

Thanks, Win7/64ISO

 

If you don't need a lot of space, an ssd is better, you get both faster read and writes, so everything loads really fast, and things such as Windows and program installations go very fast too.

The additional benefit of using just an ssd is that they are lighter, usually use less power consumption and are less likely to die in a laptop than a hard drive, hybrid or otherwise.

Imo the main reason to get a hybrid is if you need a lot of storage and don't have the space or budget to get a separate hard drive and ssd.

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The SSD's are quicker and more money. The only drawbacks to the SSD are disk space and if the SSD dies suddenly w/o warning, its like good luck with getting your data back, if possible?

With a HDD at least you can recover your data. So that's a selling point for me. I see a lot of new computers now have hybrid drives for this reason.

I don't know technically how to setup a SSD w/an external drive? Where you have the OS on the internal SSD and the data on an external disk? Or something to that effect. Then if you SSD dies suddenly, you at least have your data on the external drive.

 

Laptop hard drives can die randomly too, and they're lot more likely to die than an ssd if you're using the laptop on the go.

Realistically regardless of what kind of storage you're using, you should have a copy of your data backed up externally, whether on the cloud or with some sort of external storage such as hard drive or DVDs.

While you have a better chance of recovering data off a hard drive than ssd, depending on how the hard drive condition is, you could be spending upwards of $500 to recover the data.

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Don't get a regular mechanical disk. Get the latest Hybrid drive or an SSD (can be an older (reliable) model for cheap) for sure. Pure mechanical drives are horrible as system drives. I have used the Scorpio Black 750GB, it's not that fast. Not bad but not fast.

 

I assume that write caching firmware update is never coming, then?

 

I don't think for the 750's there was even a single firmware upgrade let alone one for the promised cache writing. If you go to the site for SSHD there is only the 28 version for the first gen 500gb drives.

 

A SSH drive is better than a standard one only if used as a primary hard drive, so commonly read data (say OS data) gets moved to the NAND. And it will still be way slower than a SSD.
If used as a secondary drive, like I do, I see zero to marginal speed improvements over my old WD Blue 750GB.