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neddy
(@neddy)
Active Member

Anyone care to speculate on the impact that this piece of kit may have on our work?

http//support.apple.com/kb/HT5446?viewlocale=en_US&locale=en_US

http//www.techradar.com/news/computing/apple/apples-fusion-drive-what-you-need-to-know-1106833

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Posted : 26/10/2012 8:23 pm
jaclaz
(@jaclaz)
Community Legend

Anyone care to speculate on the impact that this piece of kit may have on our work?

JFYI, only seemingly unrelated
http//www.forensicfocus.com/Forums/viewtopic/t=9847/

jaclaz

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Posted : 30/10/2012 12:39 am
athulin
(@athulin)
Community Legend

Anyone care to speculate on the impact that this piece of kit …

Just speculation it looks like a unit that combines one HDD and one flash drive with added logic to move files/sectors from the one to the other depending on access frequency, and possibly more. That may make it remotely RAID-like in that it presents the standatd ATA interface to its host, but it is reasonably free to do whatever it likes on the inside.

Q1 How is the multiplexing between the HDD and the SSD done? Something like the P/G lists in HDDs? That is, when the host requests a sector N, the Fusion logic decides if that sector is present on the SSD, or if the request must be passed to the HDD. That would suggest that the SSD would be little but a container for 'fast' sectors' + some kind of sector access statistics database. (A bit like those 'Shadow' devices by … was it Vogon?)

Q2 How many copies of sector N will there be? Two - one 'slow' on the HDD, and one 'fast' on the SSD? Or perhaps only one – placed according to the access frequency? Two would be easiest to implement (just stuff the sector onto the SSD as it is being read), and probably safest in general. One would be rather messy to implement.

Q3 Q1 and Q2 assumes that this is a general purpose device, serving ATA protocol to the host, and doing access statistics on sectors. Is it? or is it a very special-purpose device that relies on the file system implementation to keep track of access patterns, and issuing orders to move files (or chunks of sectors) from the HDD to the SSD, or vice versa?

If this is a general purpose device, I suspect it will not pose any additional complexity – the HDD will probably be the master copy. The SSD may contain old data, which could be useful in some contexts, say for files that are not version controlled.

If this is a special purpose device (i.e. heavily dependent on HFS+ implementation), it's as if an entirely new disk had appeared non-ATA, non-SCSI, non-anything-else. That means starting from scratch as reagrds imaging as well as interpretation.

I'd suspect it's a general-purpose device, though – it seems to make more sense from a business perspective than creating something very special only for Apple customers. On the other hand, those support answers suggest there is something special about it after all. But then again … support is usually designed to minimize customer problems than to explain actual truth.

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Posted : 30/10/2012 11:16 am
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