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Re: V5 format and man mkfs.xfs

To: Matthias Schniedermeyer <ms@xxxxxxx>,Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: V5 format and man mkfs.xfs
From: Greg Freemyer <greg.freemyer@xxxxxxxxx>
Date: Tue, 17 Jun 2014 23:39:58 -0400
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On June 17, 2014 11:29:17 AM EDT, Matthias Schniedermeyer <ms@xxxxxxx> wrote:
>On 17.06.2014 22:37, Dave Chinner wrote:
>> On Tue, Jun 17, 2014 at 10:26:51AM +0200, Matthias Schniedermeyer
>wrote:
>> > Hi
>> > 
>> > How seriously meant is "V5 isn't experimental anymore"?
>> 
>> "Fully supported" isn't a clear enough statement?
>
>I guess that was a "selective memory"-bug on my side.
>
>> > I ask because the man-page only mentions the syntax to enable it by
>
>> > accident. A.k.a. the backport of ftype to V4.
>> > (man-page of xfsprogs 3.2.0 in Debian-SID)
>> 
>> That's intentional. V5 superblocks are an implementation detail that
>> most users don't even need to know about. They care about the name
>> of the features they are enabling at mkfs time, not the details of
>> the on-disk implementation of those features.
>
>The question still stands.
>
>The crc-option is only mentioned "by accident".
>Without the ftype backport there would be no mention of the "feature 
>crc".
>
>Furthermore i suspect that the ftype-feature also wouldn't be
>mentionted 
>without the V4 backport.
>
>Which beggs the question, what other features are "burried" in V5 that 
>aren't mentioned in the man-page.
>
>And are there any other "-m" options, because "-m" (asside from the 
>ftype accident) is completly undocumented.
>
>> > And you still have to know that crc means V5.
>> 
>> Why do you care about the format mkfs.xfs chooses for you - it's
>> based on the features you requested. V5 isn't magically faster than
>
>I find the crc feature relativly important.
>
>I personally had exprienced an USB enclosure(-model. As in i had
>several 
>of those) that under rare circumstances flipped or cleared a single bit
>
>in a specific bit-pattern). Such corruption most likely ends up inside
>a 
>data-file because most times there is more data than meta-data. But 
>COULD happend inside the meta-data.
>
>Since that day i have nearly everything MD5(or SHA256)ed so i can at 
>least detect if i have a data-corruption.
>
>Fortunatly that never happend again after i replaced that enclosure 
>model. Which i can say with pretty high confidence.

I md5 hash a lot of important files.  I've seen lots of failures to verify over 
the years.  As you note, it is typically a hardware failure, but they happen 
none the less.

Recently the most common failure has been the sata cables.  They are not very 
robust if you connect/disconnect them very often.

Greg
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