[dm-crypt] Hybrid drives

Heinz Diehl htd at fancy-poultry.org
Sat Jul 17 13:45:34 CEST 2010


On 17.07.2010, Mikko Rauhala wrote: 

> > When you format the disc using "cryptsetup luksFormat", the 4 GB SSD part
> > isn't included. Please correct me if I'm wrong.
 
> You're wrong in a very confused way. The SSD never stores anything that
> wasn't on the hard disk, and only a part of that anyway. All operations
> on the disk likewise indirectly affect the SSD cache.

It's quite clear to me how the crypto layer works, and data send /written
to the SSD cache only gets there in encrypted form when the SSD part is
used as a disc cache exclusively. I'm not quite good in explaining things,
I guess :-) I'm just curious if this SSD part is "just a cache", or maybe
something else, as e.g. an additional "drive" with its one device, or a
mixture of that... That wasn't quite clear to me. There's some articles
out there which describe this SSD part as a "cache only" area, just like
the cache which commonly is used with any harddisc drive, and I've read a
report which described this area as a kind of "additional drive" which
gets used as a cache at the same time, just if you would store your linux
swap on an extra harddisk. 

Don't know if you can follow me now, blame it on me in this case, thinking
"'round the corner" :-)



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