linux-ext4 - Re: fsync() errors is unsafe and risks data loss

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Date:   Wed, 18 Apr 2018 12:52:19 -0400
From:   bfields@...ldses.org (J. Bruce Fields)
To:     Martin Steigerwald <martin@...htvoll.de>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        "Joshua D. Drake" <jd@...mandprompt.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: fsync() errors is unsafe and risks data loss

> Theodore Y. Ts'o - 10.04.18, 20:43:
> > First of all, what storage devices will do when they hit an exception
> > condition is quite non-deterministic.  For example, the vast majority
> > of SSD's are not power fail certified.  What this means is that if
> > they suffer a power drop while they are doing a GC, it is quite
> > possible for data written six months ago to be lost as a result.  The
> > LBA could potentialy be far, far away from any LBA's that were
> > recently written, and there could have been multiple CACHE FLUSH
> > operations in the since the LBA in question was last written six
> > months ago.  No matter; for a consumer-grade SSD, it's possible for
> > that LBA to be trashed after an unexpected power drop.

Pointers to documentation or papers or anything?  The only google
results I can find for "power fail certified" are your posts.

I've always been confused by SSD power-loss protection, as nobody seems
completely clear whether it's a safety or a performance feature.

--b.