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Date:	Sun, 12 Oct 2014 19:53:52 +0200
From:	squadra <squadra@...il.com>
To:	Ivan Baldo <ibaldo@...net.com.uy>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	EXT3 Users <ext3-users@...hat.com>
Subject: Re: power loss protection

dunno about any special tools, but misusing a mysql database could be
a good check for this. unplug/reset your device while inserts into the
db are ongoing (dont forget to use innodb for the tables). unplug /
reset your device, boot it up again and take a look into the mysql
log. theres a good chance that innodb gets wrecked... sure, this is
not perfect. but could be a impressive test if it ends like i think.

make sure your mysql instance is configured to be "safe":

http://dev.mysql.com/doc/refman/5.1/en/innodb-parameters.html#sysvar_innodb_flush_method
http://dev.mysql.com/doc/refman/5.1/en/innodb-parameters.html#sysvar_innodb_flush_log_at_trx_commit

and enable binlogs + sync binlogs

or in other words: make it as slow as possible :p

On Sun, Oct 12, 2014 at 4:07 PM, Ivan Baldo <ibaldo@...net.com.uy> wrote:
>     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
>
> _______________________________________________
> Ext3-users mailing list
> Ext3-users@...hat.com
> https://www.redhat.com/mailman/listinfo/ext3-users

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