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power loss protection


El 11/10/14 21:19, Theodore Ts'o escribió:
If you are running some workload which is constantly calling fsync(2),
that will be forcing journal commits, and those turn into cache flush
commands that force all state to stable storage.  Now, if you are
using CF cards that aren't guaranteed to have power-loss protection
(hint: even most consumer grade SSD's do not have power loss
protection --- you have to pay $$$ for enterprise-grade SLC SSD's to
have power loss protection --- and I'm guessing most CF cards are so
cheap that they won't make guarantees that all of their flash metadata
are saved to stable store on a power loss event) the fact that you are
constantly using fsync(2) may not be providing you with the protection
you want after a power loss event.

    This got me worried!
How can we test if a device really stores all the data safely after a barrier and sudden power loss?
    Is there a tool for that?
I am thinking something along the lines of a tool that does writes with some barriers in between and then I unplug the device and run the same tool but in a "check mode" that tells me if the requested data before the barrier is really there. Something sysadmin friendly or maybe even user friendly, but not too hard to use.
    Thanks for your insight!

Ivan Baldo - ibaldo adinet com uy - http://ibaldo.codigolibre.net/
From Montevideo, Uruguay, at the south of South America.
Freelance programmer and GNU/Linux system administrator, hire me!
Alternatives: ibaldo codigolibre net - http://go.to/ibaldo

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