HD Cache project

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axe
Posts: 7
Joined: Tue Jul 15, 2008 4:22 pm

HD Cache project

Post by axe » Fri Nov 04, 2011 9:45 pm

HI all
I heard in the last few weeks an episode on a podcast I listen to, but cant remember which one, nor have I found any show notes that would help me...

I've always thought there should be a project that would duplicate what a hybrid drive does... And I know I heard about one that does...
I thought it was something like zcomp or something. Basically it uses system memory to cache the HD reads and writes. I'd love to give my system(s) a boost. Can anyone tell me the project name?

Thanx much
Axe

deptrai
Posts: 18
Joined: Tue Aug 28, 2007 5:21 am
Location: Vietnam / Detroit
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Re: HD Cache project

Post by deptrai » Sun Nov 13, 2011 8:51 am

If by "hybrid drive" you mean one that has both flashmemory ("SSD") and spinning platters, "system memory" can't do that no matter what software you use because it's volatile and its contents are lost (nearly) as soon as the system is powered off.

If on the other hand you mean a RAM cache (which nearly all modern hard drives have), there is such a project, called "the linux kernel" (and before that, "the unix kernel"). All unix systems cache data for block-device writes to RAM before actually writing to the device, and even after a buffer has been phyically written, it may remain in the block cache until the memory is needed for something else; if a read of a block that is in the cache is requested, the data in RAM is returned without hitting the drive. The block buffer system is normally used for all block devices, regardless of filesystem type (or even use of the device for purposes other than a filesystem).

You may be thinking of an application-level cache such as memcached, but this will not help for general filesystem usage.

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