Ramdisks and hard drives as cache devices [LWN.net]

Ramdisks and hard drives as cache devices

Posted Jul 8, 2010 14:57 UTC (Thu) by etienne (subscriber, #25256)
In reply to: Ramdisks and hard drives as cache devices by butlerm
Parent article: Bcache: Caching beyond just RAM

> I imagine that Bcache caches O_DIRECT reads and writes, which could give a caching advantage even where an application has elected to bypass the ordinary buffer cache.

An application like a boot-loader installation/upgrade which tries to tell which disk sectors to load from the MBR?
I hope there is a sync() to write to (the real destination) disk.

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Ramdisks and hard drives as cache devices

Posted Jul 8, 2010 23:19 UTC (Thu) by koverstreet (subscriber, #4296) [Link]

Bootloaders are a special situation - the most practical thing to do would be to just not enable write behind caching for /boot. For everything else, sync happens when you switch off write behind caching, and sync without switching it off doesn't really make any sense, the cached device is going to be inconsistent as long as write behind caching is on.