

Fusion Drive: Apple jumps on the SSD cache bandwagon - evo_9
http://www.extremetech.com/computing/138535-fusion-drive-apple-jumps-on-the-ridiculously-overpriced-ssd-cache-bandwagon

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headShrinker
"Update: After poking at this more, it’s possible that Apple is using a
simplified tier structure in which entire files are moved to the SSD and
backed up the HDD, rather than a more sophisticated caching mechanism."

Sensational blog post. Extremetech couldn't be troubled to follow through with
due diligence, it apparently doesn't have any journalistic integrity, or
editorial review. They literally falsely accuse a company (right in the blog
title) of releasing an overpriced commonly available product. Then, at the end
of the article excuse their horrible research, by starting with the sentance
"it’s possible that Apple". Shouldn't Extremetech know what Apple is doing
since you just finished writing a scathing blog post about it??

In fact, they are not caching at all. Extremetech completely blew it on this
article, either revealing their lack of professionalism, bias, and/or, both.

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wmf
Apple's charging $250 for a $99 SSD plus some software. It's overpriced.

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jonknee
Welcome to Apple's SSD pricing. Want to upgrade from 128GB SSD on a laptop to
256? $300 for that please. How about from 128GB to 512GB? $800. All the way to
an astounding $1,300 for a 768GB drive. It's insanity, but since you can't
open up the laptops to add one of your own it's insanity that you have to pay
for.

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fruchtose
I really hope you don't have to pay $1,300 to get a 768GB drive in your
system. I ran into a situation a couple years ago when the 320GB drive in my
MBP was running out of space. I didn't want to buy a whole new system, so I
ordered a 640GB drive online, took it to a local certified Apple repair shop,
and let them put the drive in. The cost of the work? $100.

This was before the unibody models, but I'm sure the process will be the same
for the new systems. Oh, and the best part of going to an Apple repair shop
was that my warranty remained intact. I never had any issues getting the Apple
Store to work on my laptop after the hard drive was replaced.

If Apple prevents people from doing this with the new hardware, then this will
be a disappointment. I haven't kept up with the specifics of their new laptops
--I know that the RAM is soldered in, but I hope the hard drive will be
replaceable.

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evilduck
AFAIK on the latest Apple models with SSDs, the SSDs are a proprietary form
factor but not soldered on.

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barredo
Edit: Alright, they updated the blogpost saying this.

But it's not an SSD 'cache' right? It's two separate disks/units merged by the
OS. Not like Intel, OCZ, etc which is an HDD with some SSD chips "before the
bus", Right?

<http://s2.gizmologia.com/files/2011/06/2011-05-31-ocz.jpg>

Or I am missing out?

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Lagged2Death
_It's two separate disks/units merged by the OS._

That's my understanding, and in fact I expect that would make it work better
in some ways.

But if that's so - if it's two commodity pieces of hardware managed by some
driver-level software - then it would make sense for it to be _cheaper_ than
the custom-hardware solutions from other sources. Or at least, we might expect
the per-unit cost to Apple to be lower than the custom hardware systems.

So that just makes the alleged overpricing worse.

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mbreese
It would only be cheaper if the components were the same. My Seagate hybrid
drive has somwthing like 4-8GB of flash. Doesn't the Apple hybrid have 128GB?

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Lagged2Death
Yes, 128GB for $250. But excellent 128GB SSDs can be had _at retail_ for as
little as ~$90 on sale. What does that 128GB drive - purchased in huge
quantities directly from the manufacturer - cost Apple?

Your Seagate hybrid isn't the only system of it's kind, it's not the
comparison I had in mind.

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simonh
In practical terms last week if you wanted a Flash+HDD solution from apple it
cost about $500 to add a 256GB flash drive and 1GB hard disk (I can't remember
exactly, and anyway I'm more familiar with UK prices). Now you can get a
fusion drive for $250.

They're not directly comparable technically, but I'm in the market for a 27"
iMac. The cost of the optimum available spec for me just went down and the
convenience went up, so I'm a happy camper.

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adsr
It sounds more like tiered storage than cache to me, or perhaps it's both. But
why let that get in the way of a sensational headline.

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damon_c
It sounds like a huge improvement over my current workflow of having my OS and
Apps on the SSD and then having symlinks to my old larger hard drive for all
my photos and videos.

Has this sort of thing really existed on Windows for years or are people just
seeing the words "flash" and "cache" and oversimplifying it?

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r00fus
Intel's Z68 SRT has existed some time with windows-only drivers, but it's not
clear how Apple's fusion drive compares in functionality, portability or
performance with an equivalently specced SRT-drive (ie, a 128GB SSD used as
the cache drive in a windows box).

A detailed review + teardown will able to answer these questions.

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vinothgopi
Well you cant call it caching. By definition, that means data is written to
both drives at the same time. In the case of Fusion Drive data is always read
from and written to the SSD. It is basically a software which moves files
around.

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luu
_Well you cant call it caching. By definition, that means data is written to
both drives at the same time._

Writing data to both the cache and the main store is not a fundamental
property of caches. Consider, for example, the caches on the microprocessor of
an x86 chip. The only time both the cache and main memory will contain the
same data is if the trait is set to 'WT', which is very rare.

It's true that (coherent) caches behave in such a way that you can't tell that
the data isn't duplicated at each level, but that's achieved by writing back
the data when, for example, an external device requests some particular cached
data.

If the cache is persistent, and external devices can access the cache as
easily as the main store, there's no particular reason to write data back,
other than evictions [1], i.e., you should expect the cache to basically be "a
software which moves files around"

[1] This isn't strictly true -- depending on the access patterns and the
characteristics of the cache and the bus, you might want to opportunistically
write data back to avoid having to write back on an eviction. Disclaimer: I've
only worked on microprocessor caches and not disk caches, so I'm not
intimately familiar with performance traces for disk caches. However, based on
simple back-of-the envelope reasoning, it seems to make sense to make disk
caches the type of cache you consider not to be a cache at all.

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spitfire
Which chipset does the new imac use?

Intel has SSD caching support built into the Z68 chipset now, it sounds eerily
similar, they could simply be using that. Both reads and writes are cached.

[http://www.anandtech.com/show/4329/intel-z68-chipset-
smart-r...](http://www.anandtech.com/show/4329/intel-z68-chipset-smart-
response-technology-ssd-caching-review/2)

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wmf
There's actually nothing built into the chipset; Intel RST is a Windows driver
(it just refuses to run on any chipset that it doesn't like). RST behaves
fairly differently from descriptions of Fusion Drive.

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spitfire
Alright, I was under the impression it was a partial hardware implementation.
I knew that it was artificially restricted to the Z68 chipset only, but still
thought it was sort of a winmodem type solution.

IE: there's still some special hardware there but the real smarts was in the
driver.

I stand corrected. Regardless, this is only a stopgap solution while SSD
prices fall. I expect to see it MIA in 2-3 generations.

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Shivetya
I just want to know, can I override its behavior so as to favor applications
or directories I want better throughput with.

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wmf
Nope; no ricing allowed.

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jonknee
I'd love it if they would introduce support for it outside of the BTO option.
I'd like to rip out my optical drive and put in an SSD, but the pain of having
to transition everything over has so far kept me from doing so.

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Toshio
This idea originated from technology that has existed in advanced storage
arrays for awhile, and in fact ZFS is optimized to take advantage of it.

Apple has consumerized it now.

