6 ms·

Digging Into Apple’s Fusion Drive Details

34 points by barista 14y ago

tomkinstinch 14y ago
Reminds me of Seagate's Momentus XT, except it sounds like the file management is done in the OS and not on the drive, and that the SSD is not being used as a cache. http://www.anandtech.com/show/3734/seagates-momentus-xt-review-finally-a-good-hybrid-hdd http://www.anandtech.com/show/3734/seagates-momentus-xt-revi... I'm guessing the SSD portion will be MLC? Are there any other hybrid drives like this in the wild?
- cokernel_hacker 14y ago
  This is not a hybrid drive, it is two drives as evidenced by the picture of the iMac that Phil Schiller showed. This is more akin to "tiered storage" which has existed before, just not in the consumer space which prevents more/different challenges.
  - tomkinstinch 14y ago
    I see, thanks; I haven't had a chance to watch the Keynote yet. Do you know how difficult it would be to set up something comparable using two drives (HDD+SSD) under, say, Ubuntu?
    - brian_cloutier 14y ago
      I don't know about Ubuntu, but apparently Windows Vista and 7 have something very similar. http://en.wikipedia.org/wiki/ReadyBoost http://en.wikipedia.org/wiki/ReadyBoost
      - cokernel_hacker 14y ago
        Not even sorta similar, "ReadyBoost" is a cache "Fusion Drive" provides the union of space. They are in the same vein of "hide the slowness of rotational media" but that is a pretty huge vein.
        brian_cloutier 14y ago
        In the Fusion Drive example, 3TB of hard drive is combined with 128GB of flash. The union of space is 3.125 TB, compared to the 3TB you would get with a cache. That's just a 4% increase in space that the Fusion Drive gives you over what a cache would give you. You can call it whatever you want, but I'm going to call them similar.
        cokernel_hacker 14y ago
        And "just" a 32x increase in flash size.
      - rhplus 14y ago
        Not ReadyBoost, but ReadyDrive: http://en.wikipedia.org/wiki/ReadyDrive#ReadyDrive http://en.wikipedia.org/wiki/ReadyDrive#ReadyDrive
    - fusiongyro 14y ago
      Well, if I wanted to achieve this today and I had an HDD and SSD in this computer, I'd mount /home and maybe /var on the HDD and everything else on the SSD. I usually go with a three partition setup (/boot, /, swap) and even that just with /home on the HDD would get you 3/4ths of the way there.
    - wtallis 14y ago
      There are a couple of block-level cache systems in development, but that haven't yet been accepted into the mainline kernel. The one most suited for desktop SSD+HDD use right now is bcache, which is aiming to hit the kernel staging area next year. Facebook's flashcache is the other main contender. Both offer writeback and writethrough caching, but they differ in their policies for what kind of I/O skips the cache. Bcache tries to detect sequential I/O and send that straight to the backing disk, and organizes the I/Os sent to the SSD in a manner that tries to go easy on the SSD's wear leveling and garbage collection algorithms. Flashcache, on the other hand, tries to use the SSD to cache chunks of information that fit the SSD's page size - smaller I/Os skip the cache, which is probably the exact wrong thing for desktop workloads.
- sehugg 14y ago
  I'm surprised that the benchmarks for the Momentus XT are so good, especially since it only has 4 GB (8 for the newer model) of SSD. It would seem that in theory it would be better to just add 4 or 8 GB of DRAM to your main system, but apparently the drive only caches non-sequential data that isn't likely to be read quickly from the platters. I'm thinking of trying one on my aging MacBook Pro. Anyway the Apple approach should be better because of the bigger SSD and more intelligent caching available at the OS level.
  - reeses 14y ago
    The first revision of the XT (.5TB) was a dog and barely worth the effort. The new version is significantly improved.
  - yeureka 14y ago
    I installed the 750GB/8GB Momentus XT on my late 2008 MBP and it has been a breath of fresh air. Previously I had a 500GB WD Scorpio Black. That was fast but it vibrated a lot and I think battery life was worse than with the Momentus. I mainly use the machine for XCode and Visual Studio and now I am CPU bound.
vubuntu 14y ago
It's the poor man's (or rather consumer's) 3PAR! HP 3PAR, StorSimple etc all have done it long time back but at a bigger scale. Apple is just scaling it down, and bringing it in front of the regular Joe (as regular as Apple customers tend to be) in a non-complex manner.
- cokernel_hacker 14y ago
  Tiered storage has been done before, this is true. However, they are dedicated systems. If "Fusion Drive" is at the OS level, that means it shares resources with the rest of the system which presents more/different challenges.
  - vubuntu 14y ago
    StorSimple implements auto-tiering at block level and presents an iscsi target block device transparently to the OS/Filesystem layer. It is built on top of already available open source linux iscsi target software. If Fusion was done in similar manner, it absolutely does not require any modifications to the regular OS/file system layers at all. The intelligent auto-tiering capable iSCSI target portion would be at the driver level well isolated from the rest of the OS/filesystem components. It probably even has more simplistic rules for tiering . Keep OS files/dir always on SSD. Apply tiering logic to app data using a simplistic LRU scheme. And there is only two tiers to deal with. I am no expert in Linux/iSCSI or auto-tiering, but I bet you this is something that a HP/3PAR or Dell Compellent can spin up at a very short notice using their existing technologies. Apple is very good at identifying a complex ( and in most cases an existing but end-user un-friendly) technology that has been under-utilized in consumer space and bring it down to consumer level and deliver it in a consumer-friendly manner and put a wonderful marketing spin on it with cool terminology (Retina display, Fusion drive)and possibly even patent some arcane & obvious variations of the main theme.
    - cokernel_hacker 14y ago
      StorSimple, 3PAR, etc. all appear to be appliances. What I am trying to get as is subtle so I will try to be a little bit more explicit. StorSimple can dominate the appliance it is made out of to provide its services. Fusion Drive cannot dominate the owner's machine.
bane 14y ago
This is really cool tech. Not only does it solve the problem of "having more stuff than I can fit on an SSD I can afford" but "long-term storage that I still need periodic random access to but I/O performance is not paramount, but heavens no, it needs to be faster than a tape backup"
Mythbusters 14y ago
Seems like an interesting choice not use the fast disk as a cache. This is the design that Windows 7 and beyond went with. http://technet.microsoft.com/en-us/magazine/ff356869.aspx http://technet.microsoft.com/en-us/magazine/ff356869.aspx
epistasis 14y ago
I wonder if this was implemented as a combination of LVM with an extended area for the Hot File Clustering [1], which currently reserves only 0.5% spinning boot disks for small files with a high temperature. Lots to speculate about, little to know at this point, it seems. [1] http://osxbook.com/book/bonus/misc/optimizations/#THREE http://osxbook.com/book/bonus/misc/optimizations/#THREE
ChuckMcM 14y ago
I wonder if they can do a write log to the spinning rust (sequential write, pretty fast, slow on the SSD) and then periodically resolve the deltas. I played around briefly with a system which put metadata in a RAM disk (battery backed up to SSD) and actual data blocks on the disk. There was a huge benefit in that system of splitting the metadata i/o's from the read/write I/Os, really helped overall performance. I look forward to seeing the whitepaper on this tech if they publish it.
- cynicalkane 14y ago
  ZFS uses a log-structured filesystem journal, and in my experience can do a little less than twice as many 'random' writes to a spinning hard drive than that hard drive is capable of. Of course the random writes are actually sequential. If you have a SSD log device configured, writes greater than 128k (IIRC) are sent directly to disk for performance reasons. This behavior is configurable and probably should be higher for modern SSDs... but anyway it's a neat idea that has been used in practice.
mistercow 14y ago
So they seem to be trying to differentiate this from a typical HHD (besides the fact that it's two separate devices) by saying it's "not a cache", but practically speaking, are the benefits of "not duplicating" really worth it? Sure, you get 12.5% more space that way, but it seems like the performance implications would be almost exclusively negative. On a typical HHD, under typical circumstances, all writes go to the SSD, and are copied to the HDD later on. So far so good; Apple's solution will do the same thing. And stuff being read gets copied to the SSD in both cases. Also great. Now, suppose a file is loaded to the SSD and we never write to it. Now the SSD gets full, and the file has to be moved off of the SSD to make room. On a typical HHD, all that happens is the file gets deleted from the SSD. It's still on the HDD, so no further action is necessary. But on Apple's Fusion Drive, this file will have to be copied back to the HDD. Considering that some of the largest kinds of files (e.g. videos) are exactly the sort of thing you will want to put on the SSD and not modify, this seems like a pretty terrible idea.
- ryannielsen 14y ago
  On a typical HHD, under typical circumstances, all writes go to the SSD, and are copied to the HDD later on. So far so good; Apple's solution will do the same thing. And stuff being read gets copied to the SSD in both cases. Also great. That's an assumption we've yet to see confirmed, and I suspect is incorrect. I doubt every single file that's read will migrate to the SDD. Rather, I expect only files frequently read will migrate to the SDD. Effectively, the SDD will largely be a write cache (but likely only for files written atomically) and a read cache for frequently accessed files. That behavior would largely sidestep your concerns. (And, actually, files that are readily streamed, like videos, aren't necessarily files you'd want to store on the SDD. Those can often – though, yes, not always – be read quite quickly from the HDD. Unless you're dealing with truly huge files, or actively editing a video, you don't need SDD throughput.)
  - mistercow 14y ago
    (And, actually, files that are readily streamed, like videos, aren't necessarily files you'd want to store on the SDD. Those can often – though, yes, not always – be read quite quickly from the HDD. Unless you're dealing with truly huge files, or actively editing a video, you don't need SDD throughput.) Hmm, I hadn't noticed that they're only doing this on desktops, so I was thinking there in terms of energy efficiency. On a laptop, you definitely want that video to get copied over to the SSD so that the HDD can spin down and stop draining your battery. On a desktop, I guess you wouldn't care as much.
Derbasti 14y ago
I think its funny how Apple tries to solve its file system issues with SSDs. No other popular file system will get quite as unbearably slow when in heavy use as HFS+. No other file system will just randomly create errors and little corruptions here and there in regular use. No other popular OS will come to a complete halt as soon as it starts swapping because its file system can't handle it. And instead of fixing that stuff, Apple is pushing SSDs to everyone. Way of the future.
- taligent 14y ago
  Sorry but none of what you said is true. There may be bugs and bugs in the past. But there is no systemic "this FS will lose data under heavy use" design fault. If there was then millions of people would have been affected. And of course Apple is pushing SSD to fix a FS bug not because it is 10x faster and 1/4 the size of a mobile HDD.
  - Derbasti 14y ago
    HFS is producing errors all the time. Run Disk Utility to see them. They may not be fatal, but they happen. Apple computers with HDDs do get unusably slow once they start swapping. So much so that it is usually impossible to terminate the memory-hungry application. With SSDs the computer becomes usable again. Just ask some plastic MacBook users. So, what exactly is untrue about what I said? Just claiming that it is not is not very productive.
    - Synaesthesia 14y ago
      I've owned plenty of Macs, even my G4 with 256mb RAM was still usable, surprisingly, under Tiger. Generally I didn't find it to have the issue you mention, or find it slower than windows Of course SSD's have a benefit. But I think your particular MacBook may have had a failing drive.
    - ryannielsen 14y ago
      So, what exactly is untrue about what I said? Potentially nothing, but it is all anecdotal. Where's the widespread or researched evidence of HFS (especially in its HFS+ or HFSX variants) being a slow and easily corruptible file system? It's not like HFS is a rare and infrequently used file system – it's the primary filesystem for all Macs since System 3, for many iPods, and for all iOS devices. The scaling limits present in HFS+ will rarely be hit by most users and, while not as resilient as more modern FSs, there are no inherent fatal design flaws with HFS that I'm aware of. Perhaps you've pushed HFS+ beyond its limits, or have usage patterns that trigger a rare fatal bug, but just claiming that something is true is not very productive either.
owenfi 14y ago
I wonder if it's this: http://en.wikipedia.org/wiki/Smart_Response_Technology http://en.wikipedia.org/wiki/Smart_Response_Technology Oh, it's probably not, because that page says the maximum size is 64GB. (I work @ Intel and have no inside knowledge about this feature at all.)
cbsmith 14y ago
"There are other hybrid models of blending SSD and mechanical disks to save money, but none of them are able to integrate with the OS and do it as intelligently as Apple is able to with Fusion Drive." Seriously? Aside from hybrid drives, Windows has had a very similar technology since Vista (SSD's weren't as inexpensive back then, so it wasn't terribly well received), and of course there is ZFS with it's L2ARC. The whole "it's not a cache" thing is a canard. Doing it right means doing it much like swap: you may have dupes in certain cases. Going beyond that actually hurts performance.
- ryannielsen 14y ago
  The whole "it's not a cache" thing is a canard. Doing it right means doing it much like swap: you may have dupes in certain cases. Going beyond that actually hurts performance. It's fundamentally not a cache. If it were a cache, Fusion Drive would not increase the total storage space. Anandtech[1] seems to confirm this, noting that Fusion Drive creates a 4GB write buffer on the SSD and all read operations will influence a pinning algorithm which will move, not cache, frequently accessed files from the HDD onto the SSD. ReadyBoost is exactly a cache, as is ZFS's ARC and L2ARC. Now then, regarding the statement you question… yes, it is incorrect. ReadyBoost and L2ARC are pre-existing examples of "hybrid models of blending SSD and mechanical disks" that "integrate with the OS" and do so quite intelligently. You are correct to call out that statement. But it really does appear that Fusion Drive is not a cache, but a true unioning of SSDs and HDDs managed by the OS to ensure hot files are on the SSD whenever possible. [1] http://www.anandtech.com/show/6406/understanding-apples-fusion-drive http://www.anandtech.com/show/6406/understanding-apples-fusi...
  - BitMastro 14y ago
    It looks to me more like a smart UnionFS. Clever!
  - rhplus 14y ago
    The hybrid drive feature in Vista was ReadyDrive, not ReadyBoost. It never took off due to lack of driver support from manufacturers and/or Microsoft. Even so, you're right that techically it's a cache because copies are stored on both physical drives backing the logical one. I just wanted to point out that ReadyBoost was about using additional drives to use as caches, while ReadyDrive was about using hybrid drives. http://en.wikipedia.org/wiki/ReadyDrive#ReadyDrive http://en.wikipedia.org/wiki/ReadyDrive#ReadyDrive http://msdn.microsoft.com/en-us/library/windows/hardware/gg463388.aspx http://msdn.microsoft.com/en-us/library/windows/hardware/gg4...

34 points by barista 14y ago

Reminds me of Seagate's Momentus XT, except it sounds like the file management is done in the OS and not on the drive, and that the SSD is not being used as a cache. http://www.anandtech.com/show/3734/seagates-momentus-xt-review-finally-a-good-hybrid-hdd http://www.anandtech.com/show/3734/seagates-momentus-xt-revi... I'm guessing the SSD portion will be MLC? Are there any other hybrid drives like this in the wild?

cokernel_hacker 14y ago
This is not a hybrid drive, it is two drives as evidenced by the picture of the iMac that Phil Schiller showed. This is more akin to "tiered storage" which has existed before, just not in the consumer space which prevents more/different challenges.
- tomkinstinch 14y ago
  I see, thanks; I haven't had a chance to watch the Keynote yet. Do you know how difficult it would be to set up something comparable using two drives (HDD+SSD) under, say, Ubuntu?
  - brian_cloutier 14y ago
    I don't know about Ubuntu, but apparently Windows Vista and 7 have something very similar. http://en.wikipedia.org/wiki/ReadyBoost http://en.wikipedia.org/wiki/ReadyBoost
    - cokernel_hacker 14y ago
      Not even sorta similar, "ReadyBoost" is a cache "Fusion Drive" provides the union of space. They are in the same vein of "hide the slowness of rotational media" but that is a pretty huge vein.
      - brian_cloutier 14y ago
        In the Fusion Drive example, 3TB of hard drive is combined with 128GB of flash. The union of space is 3.125 TB, compared to the 3TB you would get with a cache. That's just a 4% increase in space that the Fusion Drive gives you over what a cache would give you. You can call it whatever you want, but I'm going to call them similar.
        cokernel_hacker 14y ago
        And "just" a 32x increase in flash size.
    - rhplus 14y ago
      Not ReadyBoost, but ReadyDrive: http://en.wikipedia.org/wiki/ReadyDrive#ReadyDrive http://en.wikipedia.org/wiki/ReadyDrive#ReadyDrive
  - fusiongyro 14y ago
    Well, if I wanted to achieve this today and I had an HDD and SSD in this computer, I'd mount /home and maybe /var on the HDD and everything else on the SSD. I usually go with a three partition setup (/boot, /, swap) and even that just with /home on the HDD would get you 3/4ths of the way there.
  - wtallis 14y ago
    There are a couple of block-level cache systems in development, but that haven't yet been accepted into the mainline kernel. The one most suited for desktop SSD+HDD use right now is bcache, which is aiming to hit the kernel staging area next year. Facebook's flashcache is the other main contender. Both offer writeback and writethrough caching, but they differ in their policies for what kind of I/O skips the cache. Bcache tries to detect sequential I/O and send that straight to the backing disk, and organizes the I/Os sent to the SSD in a manner that tries to go easy on the SSD's wear leveling and garbage collection algorithms. Flashcache, on the other hand, tries to use the SSD to cache chunks of information that fit the SSD's page size - smaller I/Os skip the cache, which is probably the exact wrong thing for desktop workloads.
sehugg 14y ago
I'm surprised that the benchmarks for the Momentus XT are so good, especially since it only has 4 GB (8 for the newer model) of SSD. It would seem that in theory it would be better to just add 4 or 8 GB of DRAM to your main system, but apparently the drive only caches non-sequential data that isn't likely to be read quickly from the platters. I'm thinking of trying one on my aging MacBook Pro. Anyway the Apple approach should be better because of the bigger SSD and more intelligent caching available at the OS level.
- reeses 14y ago
  The first revision of the XT (.5TB) was a dog and barely worth the effort. The new version is significantly improved.
- yeureka 14y ago
  I installed the 750GB/8GB Momentus XT on my late 2008 MBP and it has been a breath of fresh air. Previously I had a 500GB WD Scorpio Black. That was fast but it vibrated a lot and I think battery life was worse than with the Momentus. I mainly use the machine for XCode and Visual Studio and now I am CPU bound.

vubuntu 14y ago

It's the poor man's (or rather consumer's) 3PAR! HP 3PAR, StorSimple etc all have done it long time back but at a bigger scale. Apple is just scaling it down, and bringing it in front of the regular Joe (as regular as Apple customers tend to be) in a non-complex manner.

cokernel_hacker 14y ago
Tiered storage has been done before, this is true. However, they are dedicated systems. If "Fusion Drive" is at the OS level, that means it shares resources with the rest of the system which presents more/different challenges.
- vubuntu 14y ago
  StorSimple implements auto-tiering at block level and presents an iscsi target block device transparently to the OS/Filesystem layer. It is built on top of already available open source linux iscsi target software. If Fusion was done in similar manner, it absolutely does not require any modifications to the regular OS/file system layers at all. The intelligent auto-tiering capable iSCSI target portion would be at the driver level well isolated from the rest of the OS/filesystem components. It probably even has more simplistic rules for tiering . Keep OS files/dir always on SSD. Apply tiering logic to app data using a simplistic LRU scheme. And there is only two tiers to deal with. I am no expert in Linux/iSCSI or auto-tiering, but I bet you this is something that a HP/3PAR or Dell Compellent can spin up at a very short notice using their existing technologies. Apple is very good at identifying a complex ( and in most cases an existing but end-user un-friendly) technology that has been under-utilized in consumer space and bring it down to consumer level and deliver it in a consumer-friendly manner and put a wonderful marketing spin on it with cool terminology (Retina display, Fusion drive)and possibly even patent some arcane & obvious variations of the main theme.
  - cokernel_hacker 14y ago
    StorSimple, 3PAR, etc. all appear to be appliances. What I am trying to get as is subtle so I will try to be a little bit more explicit. StorSimple can dominate the appliance it is made out of to provide its services. Fusion Drive cannot dominate the owner's machine.

bane 14y ago

This is really cool tech. Not only does it solve the problem of "having more stuff than I can fit on an SSD I can afford" but "long-term storage that I still need periodic random access to but I/O performance is not paramount, but heavens no, it needs to be faster than a tape backup"

Mythbusters 14y ago

Seems like an interesting choice not use the fast disk as a cache. This is the design that Windows 7 and beyond went with. http://technet.microsoft.com/en-us/magazine/ff356869.aspx http://technet.microsoft.com/en-us/magazine/ff356869.aspx

epistasis 14y ago

I wonder if this was implemented as a combination of LVM with an extended area for the Hot File Clustering [1], which currently reserves only 0.5% spinning boot disks for small files with a high temperature. Lots to speculate about, little to know at this point, it seems. [1] http://osxbook.com/book/bonus/misc/optimizations/#THREE http://osxbook.com/book/bonus/misc/optimizations/#THREE

ChuckMcM 14y ago

I wonder if they can do a write log to the spinning rust (sequential write, pretty fast, slow on the SSD) and then periodically resolve the deltas. I played around briefly with a system which put metadata in a RAM disk (battery backed up to SSD) and actual data blocks on the disk. There was a huge benefit in that system of splitting the metadata i/o's from the read/write I/Os, really helped overall performance. I look forward to seeing the whitepaper on this tech if they publish it.

cynicalkane 14y ago
ZFS uses a log-structured filesystem journal, and in my experience can do a little less than twice as many 'random' writes to a spinning hard drive than that hard drive is capable of. Of course the random writes are actually sequential. If you have a SSD log device configured, writes greater than 128k (IIRC) are sent directly to disk for performance reasons. This behavior is configurable and probably should be higher for modern SSDs... but anyway it's a neat idea that has been used in practice.

mistercow 14y ago

So they seem to be trying to differentiate this from a typical HHD (besides the fact that it's two separate devices) by saying it's "not a cache", but practically speaking, are the benefits of "not duplicating" really worth it? Sure, you get 12.5% more space that way, but it seems like the performance implications would be almost exclusively negative. On a typical HHD, under typical circumstances, all writes go to the SSD, and are copied to the HDD later on. So far so good; Apple's solution will do the same thing. And stuff being read gets copied to the SSD in both cases. Also great. Now, suppose a file is loaded to the SSD and we never write to it. Now the SSD gets full, and the file has to be moved off of the SSD to make room. On a typical HHD, all that happens is the file gets deleted from the SSD. It's still on the HDD, so no further action is necessary. But on Apple's Fusion Drive, this file will have to be copied back to the HDD. Considering that some of the largest kinds of files (e.g. videos) are exactly the sort of thing you will want to put on the SSD and not modify, this seems like a pretty terrible idea.

ryannielsen 14y ago
On a typical HHD, under typical circumstances, all writes go to the SSD, and are copied to the HDD later on. So far so good; Apple's solution will do the same thing. And stuff being read gets copied to the SSD in both cases. Also great. That's an assumption we've yet to see confirmed, and I suspect is incorrect. I doubt every single file that's read will migrate to the SDD. Rather, I expect only files frequently read will migrate to the SDD. Effectively, the SDD will largely be a write cache (but likely only for files written atomically) and a read cache for frequently accessed files. That behavior would largely sidestep your concerns. (And, actually, files that are readily streamed, like videos, aren't necessarily files you'd want to store on the SDD. Those can often – though, yes, not always – be read quite quickly from the HDD. Unless you're dealing with truly huge files, or actively editing a video, you don't need SDD throughput.)
- mistercow 14y ago
  (And, actually, files that are readily streamed, like videos, aren't necessarily files you'd want to store on the SDD. Those can often – though, yes, not always – be read quite quickly from the HDD. Unless you're dealing with truly huge files, or actively editing a video, you don't need SDD throughput.) Hmm, I hadn't noticed that they're only doing this on desktops, so I was thinking there in terms of energy efficiency. On a laptop, you definitely want that video to get copied over to the SSD so that the HDD can spin down and stop draining your battery. On a desktop, I guess you wouldn't care as much.

Derbasti 14y ago

I think its funny how Apple tries to solve its file system issues with SSDs. No other popular file system will get quite as unbearably slow when in heavy use as HFS+. No other file system will just randomly create errors and little corruptions here and there in regular use. No other popular OS will come to a complete halt as soon as it starts swapping because its file system can't handle it. And instead of fixing that stuff, Apple is pushing SSDs to everyone. Way of the future.

taligent 14y ago
Sorry but none of what you said is true. There may be bugs and bugs in the past. But there is no systemic "this FS will lose data under heavy use" design fault. If there was then millions of people would have been affected. And of course Apple is pushing SSD to fix a FS bug not because it is 10x faster and 1/4 the size of a mobile HDD.
- Derbasti 14y ago
  HFS is producing errors all the time. Run Disk Utility to see them. They may not be fatal, but they happen. Apple computers with HDDs do get unusably slow once they start swapping. So much so that it is usually impossible to terminate the memory-hungry application. With SSDs the computer becomes usable again. Just ask some plastic MacBook users. So, what exactly is untrue about what I said? Just claiming that it is not is not very productive.
  - Synaesthesia 14y ago
    I've owned plenty of Macs, even my G4 with 256mb RAM was still usable, surprisingly, under Tiger. Generally I didn't find it to have the issue you mention, or find it slower than windows Of course SSD's have a benefit. But I think your particular MacBook may have had a failing drive.
  - ryannielsen 14y ago
    So, what exactly is untrue about what I said? Potentially nothing, but it is all anecdotal. Where's the widespread or researched evidence of HFS (especially in its HFS+ or HFSX variants) being a slow and easily corruptible file system? It's not like HFS is a rare and infrequently used file system – it's the primary filesystem for all Macs since System 3, for many iPods, and for all iOS devices. The scaling limits present in HFS+ will rarely be hit by most users and, while not as resilient as more modern FSs, there are no inherent fatal design flaws with HFS that I'm aware of. Perhaps you've pushed HFS+ beyond its limits, or have usage patterns that trigger a rare fatal bug, but just claiming that something is true is not very productive either.

owenfi 14y ago

I wonder if it's this: http://en.wikipedia.org/wiki/Smart_Response_Technology http://en.wikipedia.org/wiki/Smart_Response_Technology Oh, it's probably not, because that page says the maximum size is 64GB. (I work @ Intel and have no inside knowledge about this feature at all.)

cbsmith 14y ago

"There are other hybrid models of blending SSD and mechanical disks to save money, but none of them are able to integrate with the OS and do it as intelligently as Apple is able to with Fusion Drive." Seriously? Aside from hybrid drives, Windows has had a very similar technology since Vista (SSD's weren't as inexpensive back then, so it wasn't terribly well received), and of course there is ZFS with it's L2ARC. The whole "it's not a cache" thing is a canard. Doing it right means doing it much like swap: you may have dupes in certain cases. Going beyond that actually hurts performance.

ryannielsen 14y ago
The whole "it's not a cache" thing is a canard. Doing it right means doing it much like swap: you may have dupes in certain cases. Going beyond that actually hurts performance. It's fundamentally not a cache. If it were a cache, Fusion Drive would not increase the total storage space. Anandtech[1] seems to confirm this, noting that Fusion Drive creates a 4GB write buffer on the SSD and all read operations will influence a pinning algorithm which will move, not cache, frequently accessed files from the HDD onto the SSD. ReadyBoost is exactly a cache, as is ZFS's ARC and L2ARC. Now then, regarding the statement you question… yes, it is incorrect. ReadyBoost and L2ARC are pre-existing examples of "hybrid models of blending SSD and mechanical disks" that "integrate with the OS" and do so quite intelligently. You are correct to call out that statement. But it really does appear that Fusion Drive is not a cache, but a true unioning of SSDs and HDDs managed by the OS to ensure hot files are on the SSD whenever possible. [1] http://www.anandtech.com/show/6406/understanding-apples-fusion-drive http://www.anandtech.com/show/6406/understanding-apples-fusi...
- BitMastro 14y ago
  It looks to me more like a smart UnionFS. Clever!
- rhplus 14y ago
  The hybrid drive feature in Vista was ReadyDrive, not ReadyBoost. It never took off due to lack of driver support from manufacturers and/or Microsoft. Even so, you're right that techically it's a cache because copies are stored on both physical drives backing the logical one. I just wanted to point out that ReadyBoost was about using additional drives to use as caches, while ReadyDrive was about using hybrid drives. http://en.wikipedia.org/wiki/ReadyDrive#ReadyDrive http://en.wikipedia.org/wiki/ReadyDrive#ReadyDrive http://msdn.microsoft.com/en-us/library/windows/hardware/gg463388.aspx http://msdn.microsoft.com/en-us/library/windows/hardware/gg4...