Fusion drive...

[Swiftylee1972]

Hi I have got a Mac mini with a fusion drive coming tomorrow,,,

Has anyone had one apart yet...

What I want to know is is it one drive or two in the machine as I have a spare hybrid drive here on me desk...

Any help would be great

 

[opinio]

Two drives. A 128 Gb SSD and a 1 Tb platter HDD. So you have no spare internal bays.

 

[Swiftylee1972]

Great not is it a 7200rpm drive or a 5400 normal slow drive ...

May rip it out and try and fuse 750gb hybrid and ssd together...

 

[opinio]

Great not is it a 7200rpm drive or a 5400 normal slow drive ...

May rip it out and try and fuse 750gb hybrid and ssd together...

It's a 5400 but fast for a 5400 historically speaking.

See http://www.tomshardware.com/reviews/notebook-hard-drive-review,3270-3.html

That review suggests it is faster than the seagate momentous xt.

I have seen some posts on the forum about using a hybrid in a fusion. Not sure if it is ok or not. Might want to ask that question first.

I have run a 5400 and the latest 7200 HSGT 1tb in a fusion and there is little difference because of the way a fusion drive works.

 

[Mike in Kansas]

Great not is it a 7200rpm drive or a 5400 normal slow drive ...

May rip it out and try and fuse 750gb hybrid and ssd together...

This fallacy needs to die.... rotational speed is hardly the most important attribute when comparing the performance of various drives. And even the "slow" 5400 RPM drives of today blow the "fast" 7200 RPM drives of just a couple of years ago out of the water; some of the current ones too in fact.

Kinda like camera megapixel wars.... another over-hyped attribute.

 

[benwiggy]

What I want to know is is it one drive or two in the machine as I have a spare hybrid drive here on me desk...

A Fusion drive is not the same as a hybrid drive. It's not caching.
It is a very clever SOFTWARE feature.

It takes an SSD and an HDD, creates one volume (a bit like a RAID 0), and then moves file blocks (i.e. smaller units than files) between the two, putting frequently accessed data on the SSD and the rest on the HDD.

As most people use probably 20% of the data 80% of the time, this works very well. The other advantage is that it can split data across the devices while maintaining file hierarchies. (E.g. say you have a large library of instrument samples for Logic. They all have to be in /Library/Application Support/Logic, but the software can move the ones you use (and don't use) to the relevant hardware.

There is nothing special or different about the hardware: it's just one SSD and one HDD. The magic is all in software.

If you already have a Fusion drive, there's not point in removing the 1Tb drive and replacing it with a 750Gb drive, even if it's slightly faster because it does caching.

 

[blanka]

And even the "slow" 5400 RPM drives of today blow the "fast" 7200 RPM drives of just a couple of years ago out of the water; some of the current ones too in fact.

My todays slow 5400 is blown away by my todays 7200. More quiet and cool too.

 

[Bohab]

A Fusion drive is not the same as a hybrid drive. It's not caching.

Yes it is.
OSX writes everything to the SSD then keeps the most frequently used files on the SSD and moves old files to the HD to make space on the SSD as its needed.

The SSD is just functioning as an extended capacity cache.

 

[ItsATrap!]

A Fusion drive is not the same as a hybrid drive. It's not caching.

Yes it is.
OSX writes everything to the SSD then keeps the most frequently used files on the SSD and moves old files to the HD to make space on the SSD as its needed.

The SSD is just functioning as an extended capacity cache.

 

[Mike in Kansas]

Yes it is.
OSX writes everything to the SSD then keeps the most frequently used files on the SSD and moves old files to the HD to make space on the SSD as its needed.

The SSD is just functioning as an extended capacity cache.

Wrong. A cache writes EVERYthing to its associated HDD, a FD does not. AND FD manages things at the block level, NOT at the file level. Complex files and packages can be split over both drives based on use. AND an FD can write blocks BACK to the SSD if they are used often, which a cache can't do. AND an FD can be read directly from the SSD, whereas in a cache arrangement the HDD writes to the cache and the out from there.

Any other way the SSD is just functioning as an extended capacity cache?

 

[benwiggy]

The SSD is just functioning as an extended capacity cache.

A cache is a temporary, duplicate copy for subsequent retrieval. That's not what the SSD's role is at all.

Fusion Drive is a form of hierarchical storage management called tiered storage.

 

[Mike in Kansas]

Yes it is.
OSX writes everything to the SSD then keeps the most frequently used files on the SSD and moves old files to the HD to make space on the SSD as its needed.

The SSD is just functioning as an extended capacity cache.

Rather than getting into a debate with me, take it up with the many tech experts who have been reporting on, and using, FD for many months. Here's just 1 such article.

http://anandtech.com/show/6679/a-month-with-apples-fusion-drive

 

[blanka]

Complex files and packages can be split over both drives based on use.

So if one part of the Fusion fails, the whole drive fails, or can you read out any half of it?

 

[benwiggy]

So if one part of the Fusion fails, the whole drive fails, or can you read out any half of it?

It's likely that the entire volume will be unreadable. Same as RAID 0.

That's why we have backups.

 

[Willis]

Yes it is.
OSX writes everything to the SSD then keeps the most frequently used files on the SSD and moves old files to the HD to make space on the SSD as its needed.

The SSD is just functioning as an extended capacity cache.

The SSD in fusion drive fills up FIRST before anything hits the HDD. So if you constantly have 200GB on your machine, they all live on the fusion drive. If you have 500GB, most used files are moved forward (as previously described very well by others) to the SSD. That's the most layman explanation I can think of!

So if one part of the Fusion fails, the whole drive fails, or can you read out any half of it?

It's likely that the entire volume will be unreadable. Same as RAID 0.

That's why we have backups.

Correct. The only way to fix a broken fusion drive is to wipe, repartition and set up again. In extreme cases you need to venture into terminal to fix the problem (file miscounts). Core storage is quite delicate and if it fails, it's extremely difficult (not impossible as I managed to recover data for a client) to get the data off the drive.

There's only one rule to owning a Fusion Drive. BACKUP AT ALL TIMES!

 

[opinio]

It's likely that the entire volume will be unreadable. Same as RAID 0.

That's why we have backups.

It is more like JBOD not RAID 0. It is not at all stripping across the two drives, and is written to the SSD first and the HDD second when the SSD is full from my understanding. then the intelligent OSX management comes into play with a 5% buffer on the SSD, block level movement etc. When i replaced a 5400 1TB from a FD with a newer 7200 1TB, the old SSD part of the FD was still bootable after the 'operation'. I was surprised! I had to erase the SSD to rebuild the FD from scratch because disk util (GUI not Command) told me I had an FD even though the new HDD was not part of it! It was like it had had a frontal lobotomy and was still working even though half the brain was missing.

 

[benwiggy]

It is more like JBOD not RAID 0. It is not at all stripping across the two drives, and is written to the SSD first and the HDD second when the SSD is full from my understanding. then the intelligent OSX management comes into play with a 5% buffer on the SSD, block level movement etc.

Yes, I know Fusion isn't the same as RAID 0. I was saying that if one device fails, then the result is the same for both technologies. Your experience shows that you still need to replace the drive and repartition.

There's only one rule to owning a Fusion Drive. BACKUP AT ALL TIMES!

The word "Fusion" is unnecessary in that sentence. All storage devices can fail, and you need a backup for all of them.

 

[ItsATrap!]

Wrong. A cache writes EVERYthing to its associated HDD.

Sorry, that is not true. Extended capacity cache systems, like Fusion, write everything to the SSD then move it to the HD as needed.
In this case, the cache SSD is larger than normal to give the OS time to determine what should stay on the SSD so that it always feels "fast", not just giving fast write times like a traditional cache.

AND FD manages things at the block level, NOT at the file level.

As does OS soft-RAID.

A cache is a temporary, duplicate copy for subsequent retrieval. That's not what the SSD's role is at all.

Per Apple.

cache |ka sh |
noun
• (also cache memory) Computing an auxiliary memory from which high-speed retrieval is possible.

The SSD in fusion drive fills up FIRST before anything hits the HDD. So if you constantly have 200GB on your machine, they all live on the fusion drive. If you have 500GB, most used files are moved forward (as previously described very well by others) to the SSD. That's the most layman explanation I can think of!

That is exactly what I said, but your description is more convoluted.

 

[Willis]

That is exactly what I said, but your description is more convoluted.

It's not a cache! It's stored there. The core OS is permanently stored on the SSD.

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The word "Fusion" is unnecessary in that sentence. All storage devices can fail, and you need a backup for all of them.

My point is that with non fusion drives you can be fairly safe that if you, for whatever reason, don't back up for a day or two, with no added data for the sake of argument, things are normally ok. In my experience with a fusion drive in a machine that was 6 days old, you'll need to keep your TM plugged in at all times (which in a desktop situation, no brainer)

But yes, no matter what storage device, SSD, HDD, FD, back up at all times.

Geez

 

[Mike in Kansas]

So if one part of the Fusion fails, the whole drive fails, or can you read out any half of it?

The whole array becomes unreadable, which is why I both clone my FD array and keep it backed up with Time Machine. Replace the failed drive, re-fuse the drives and then clone back.