linux-ext4 - power loss protection

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Date:	Sun, 12 Oct 2014 12:07:47 -0200
From:	Ivan Baldo <ibaldo@...net.com.uy>
To:	Theodore Ts'o <tytso@....edu>
CC:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	EXT3 Users <ext3-users@...hat.com>
Subject: power loss protection

     Hello.

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@...net.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@...igolibre.net - http://go.to/ibaldo

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