How do Hybrid HDD/SSD work?

How do Hybrid drives work? From what I read (I'm gonna use the Seagate Momentus XT Hybrid Drive as the example) the Seagate Momentus XT Hybrid Drive is a 750GB HDD with 8GB SSD cache. SSD cache somehow recognizes your habits and boosts speed on certain things like opening files and so on. So is the 8GB cache accesible through "My Comouter"? Because I find it redundant that you do have a SSD in the hybrid drive but it doesn't speed EVERYTHING your PC does. If the 8GB cache isn't accessible why don't manufacturers make the "X" amount of GB's accessible? I think by making it accessible and usable wouldn't it work like a desktop PC with a SSD and HDD?

 

The way it speeds things up is by preloading frequently used files and programs into the flash storage. Obviously it can't preload everything in the drive onto the 8gb flash portion.

 

couldn't they add a bigger SSD? Like a 128GB,256GB, or even a 80GB SSD would be good.

 

No, it does not prefetch based on frequently used files.

It loads up file chunks based on predictions. This gives the illusion of memory because if you open the same thing multiple times it's already in the cache and it can make more accurate predictions. That is the extent of the memory.

As soon as you open a separate file the cache is fully dedicated to that file/program.

So basically, I hit "Chrome.exe" and it starts grabbing chunks that are related to Chrome.exe. That can mean drivers or whatever.

This allows for the rather small 4-8GB to be very effective in speeding up the entire system as opposed to wasting it on a single application.

Pretty much all caching works this way btw. It's just different algorithms for cache replacement/ management.

They certainly could add a larger SSD. That would defeat the purpose though, which is to keep the drive cheap and fast.

 

The Momentus XT v1 as well as v2 both use "Adaptive Memory" technology in order to improve "READ" speeds for the drive.

Here are the nuts and bolts. ALL data is stored on the platters. You only see one main drive (500GB or 750GB). The SSD NAND flash portion is invisible and is only available internally to the drive's controller. The OS/User cannot independently write to the SSD flash, as it's purpose is to serve up blocks of data thus acting as a very fast READ-only, persistent data cache. So only frequently blocks of data on disk that do not change eventually make it into the SSD flash portion - available for any READ operation when requested. This is all handled by the XT's "Adaptive Memory" caching technology.

The XT's Adaptive Memory cache routines target frequently accessed data at the disk's block level rather than the file level, so the SSD portion is OS and filesystem independent. As more and more data blocks are requested, the drive "learns" what block addresses are being accessed over and over again, and the XT will then copy these requested blocks of data into the flash and maintain the integrity of the data b/w the SSD portion and what is stored on disk.

Also, there are some cool NEW things about the XT v2 including a feature of FAST Factor which prevents blocks storing boot-up information from being invalidated from the SSD. This means boot-ups on the XT v2 will keep all data holding blocks accessed during boot-up in READ cache, where the v1 disk may remove that data from the cache over long stretches of computer use with heavy data reads.

 

How does partitioning a hybrid drive work? Could you for example set it up so one partition had sole access to the cache, whereas the other was a simple partition?

 

So it only boosts read speeds? And it doesn't boost write speed when let's say moving a a large file to the HDD?

 

Only read speeds.

 

The drive looks like a regular 500GB / 750GB drive to the system. No special configuration, partitioning, or setup needed. It is used and accessible only by the drive itself, for caching purposes.

Think of it this way... a regular hard drive today comes with a small cache (8MB, 16MB, or 32MB). There isn't a way for you to directly access that cache. It's just there for the drive to use, based on its own internal algorithm for caching data.

A Hybrid SSD is exactly the same concept. Except instead of a small 8MB / 16MB / 32MB cache, they chose to use a 4GB cache based off of the same kind of memory chips used in SSDs (NAND flash memory).

 

No. All blocks in the drive are subject to the Adaptive Memory caching routine.

Now in the XT v2, the FAST Factor for boot stuff looks rather interesting in that it probably looks at the MBR, and follows that chain of drive reads needed to boot a system. That data is stored differently in that it cannot be invalidated by reads from disk AFTER the system has booted.

 

What would be the point of that? The idea is to bridge the gap between cheap platter drives and pure SSDs.

 

To expand on Phil's post... The WRITE goes through to the platter on disk. The drive has normal 32 MB of disk caching as well, so it may end up in pieces there while being written to the disk, but in regards to the SSD portion, no. That is not a part of the write operation. Only when you read that file in N times do the blocks of data get copied to the SSD portion available for speedy retrieval on the N+1 read.

In regards to the post about working like a HDD disk cache, it is kind of like that for READ operations, but not exactly as one read will not necessarily knock data out of the SSD portion, but READ ops will do this on the disk cache. However, it doesn't work anything like HDD cache for WRITE operations, as WRITE ops have nothing to do with the SSD NAND portion of the drive (except to maybe invalidate data stored there).

 

What I'm trying to say is that I think making the SSD bigger and accessible would work like having a double hard drive in a desktop computer and you would get the best of both worlds inside your very small laptop. And of course it would be expensive but someday the price does have to come down for consumers.

 

At that point you have a boot drive SSD that holds your OS and most used programs.

To get the performance of a proper SSD you need a controller, memory cache (sometimes) and many Storage chips. You cant fit that in along with the 2.5" notebook drive.

What you are asking for is already implemented on the Z68 desktop chipset but even then people use 30-40GB SSDs.

 

But what I'm saying is it's not possible to have that many flash chips plus the necessary hardware plus a platter drive. It's like saying "wouldn't it be great if you could fit a V8 and an I4 into a Focus, so you could have power or fuel economy when you wanted it." There are two problems, A) you can't, and B) even if you could it would be cost prohibitive.

 

Never understood these hybrid drives. HDDs arent THAT slow, I only upgraded to an SSD like 8 months ago. No point in getting a mix of the two, just save a bit more and get an SSD when possible. My two cents.

 

The point is that you get SSD like speeds for launching applications and booting at a much lower price than a SSD.

Seagate 750GB/8GB Hybrid now costs as much as 128GB SSD here.

 

The 750GB Seagate should really be 100 less but the stupid flood or whatever bumps everything up.

And there really is a noticeable difference with the NAND.

I came from a 5400RPM and oh my god it's not even funny how slow that thing feels compared to this.

I've also used 7200RPM on similar specs and there is a difference with the SSD portion.

I'm disappointed with the 8GB. I think the fast boot is a huge waste of the NAND. I don't think I'll be buying one because of that.

 

My guess is there must have been some ppl encountering problems where files used in the boot process became invalidated from the SSD Flash portion, so they added the FAST Factor - Boot stuff for XT v2 to make sure it stays in place. This would mean the XT v2 will ALWAYS boot fast, which is one selling point of the XT. However, I don't boot off my XT, so I've never had the problem.

Anyone have a guess at how much space this would take? I cannot see it being very much. I guess it would depend on what services you have running besides the OS. Still wouldn't think the size of binary files wouldn't be more than 50-70MB on the super-high end.

 

I'd heard larger. Not sure.

 

Wikipedia says that hybrid drives can operate in 2 modes: Self-Optimized Mode (where the OS thinks it's a traditional drive and doesn't realize there's an SSD acting as a cache), and Host-Optimized Mode (where the drive has commands that allow the OS or even the user to decide what gets placed in the cache).

Are there any hybrid drives nowadays that can operate in Host-Optimized Mode? How does that work - do they default to Self-Optimized Mode, but then the drive manufacturer has software that you can run to put it in Host-Optimized Mode?

 

I don't think there are any current drives (or were any drives, ever) with Host Optimized mode available.

SSHD drives are not an option in todays workflows imo; with SSD's providing the capacity and enough performance to fully replace a spinning platter, going to a 'hybrid' solution today just doesn't make sense in many/most configurations.

Just look at how old the thread is that you resurrected to see if they are pertinent anymore.

 

I didn't realize they are no longer pertinent. They still seem a lot cheaper than SSDs. You can get a 1TB hybrid drive for around $100, but you'd have to pay $400+ for a 1TB SSD drive.

Also apparently Microsoft added support for host-optimized mode into Windows 8.1, so I'd be curious to see if any drives come out with that feature.

 

The MX100 should be cheaper, at least on sale than $400...

The features you're looking for won't make a huge difference to performance.

At least not with the current SSHD's with 8GB of nand...

See:
Seagate 1TB Laptop SSHD, SATA III w/ 64MB Cache at Memory Express


That spin at 5400 RPM's (torture, anyone?).


Even the WD 1TB with it's 120GB nand is not worth the $$, even on sale, performance-wise vs. a larger capacity SSD.

See:
WD 1TB + 120GB Black² 2.5in Dual Drive, SATA III at Memory Express


Vs.

See:
Crucial MX100 Series Solid State Drive, 512GB at Memory Express



The 512GB SSD will run circles around the WD 1TB + 120G SSD (lol... I guess the drives you wanted are available! lol... but keep in mind this needs additional drivers loaded from what I have just read) and, it is less money too.


If capacity is that important to you, what I am suggesting is that buying a 7200RPM drive (Hitachi TravelStar highly recommended) is a much better option than spending more than double to get a slightly faster overall setup. The only 'real' step up is an SSD.

Even if that means one at lower capacity (for the time being); because capacity is something that can be 'fixed', while true overall performance cannot with SSHD's.


Just make sure to keep away from EVO's at this point and even the original TLC Samsung 840 models too - major issues with READS of old data.

See:
http://forum.notebookreview.com/sol...ds-old-files-evo-fix-september-19-2014-a.html


Hope I've helped a little?

(And I relearned something too...).

 

Thanks for that info! I'll definitely look to get a SSD instead of a hybrid.

 

You won't regret it.


Sent from my iPad using Tapatalk

 

I was in this mess too looking to get a SSHD or a traditional hard drive to replace my old 500GB 7200rpm one.. I went for a Hitachi 1TB travelstar as I needed the capacity at a cheap price and it was 7200rpm at the end of the day... It was also 50% cheaper then the SSHD...