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From: "Namjae Jeon" <namjae.jeon@samsung.com>
To: "'Tetsuhiro Kohada'" <kohada.t2@gmail.com>
Cc: <kohada.tetsuhiro@dc.mitsubishielectric.co.jp>,
	<mori.takahiro@ab.mitsubishielectric.co.jp>,
	<motai.hirotaka@aj.mitsubishielectric.co.jp>,
	<linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	"'Sungjong Seo'" <sj1557.seo@samsung.com>
Subject: RE: [PATCH v3] exfat: remove EXFAT_SB_DIRTY flag
Date: Thu, 13 Aug 2020 13:03:28 +0900	[thread overview]
Message-ID: <001501d67126$b3976df0$1ac649d0$@samsung.com> (raw)
In-Reply-To: <490837eb-6765-c7be-bb80-b30fe34adb55@gmail.com>

> Thanks for thinking on this complicated issue.
> 
> 
> > Most of the NAND flash devices and HDDs have wear leveling and bad sector replacement algorithms
> applied.
> > So I think that the life of the boot sector will not be exhausted first.
> 
> I'm not too worried about the life of the boot-sector.
> I'm worried about write failures caused by external factors.
> (power failure/system down/vibration/etc. during writing) They rarely occur on SD cards, but occur on
> many HDDs, some SSDs and USB storages by 0.1% or more.
Hard disk and SSD do not guarantee atomic write of a sector unit?

> Especially with AFT-HDD, not only boot-sector but also the following multiple sectors become
> unreadable.
Other file systems will also be unstable on a such HW.

> It is not possible to completely solve this problem, as long as writing to the boot-sector.
> (I think it's a exFAT's specification defect) The only effective way to reduce this problem is to
> reduce writes to the boot-sector.
exFAT's specification defect... Well..
Even though the boot sector is corrupted, It can be recovered using the backup boot sector
through fsck.
> 
> 
> > Currently the volume dirty/clean policy of exfat-fs is not perfect,
> 
> Thank you for sharing the problem with you.
> 
> 
> > but I think it behaves similarly to the policy of MS Windows.
> 
> On Windows10, the dirty flag is cleared after more than 15 seconds after all write operations are
> completed.
> (dirty-flag is never updated during the write operation continues)
> 
> 
> > Therefore,
> > I think code improvements should be made to reduce volume flag records while maintaining the current
> policy.
> 
> Current policy is inconsistent.
> As I wrote last mail, the problem with the current implementation is that the dirty-flag may not be
> cleared after the write operation.(even if sync is enabled or disabled) Because, some write operations
> clear the dirty-flag but some don't clear.
> Unmount or sync command is the only way to ensure that the dirty-flag is cleared.
> This has no effect on clearing the dirty-flag after a write operations, it only increases risk of
> destroying the boot-sector.
>   - Clear the dirty-flag after every write operation.
>   - Never clear the dirty-flag after every write operation.
> Unless unified to either one,  I think that sync policy cannot be consistent.
> 
> How do you think?
> 
> 
> BR
> ---
> etsuhiro Kohada <kohada.t2@gmail.com>



  reply	other threads:[~2020-08-13  4:03 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20200616021816epcas1p44b0833f14bbad0e25cc0efb27fb2ebd3@epcas1p4.samsung.com>
2020-06-16  2:18 ` Tetsuhiro Kohada
2020-06-16 23:55   ` Namjae Jeon
2020-06-17  7:20   ` Sungjong Seo
2020-06-17  8:41     ` Namjae Jeon
2020-06-18  8:36     ` Tetsuhiro Kohada
2020-06-18 13:11       ` Sungjong Seo
2020-06-19  4:22         ` Tetsuhiro Kohada
2020-07-10  7:36         ` Tetsuhiro Kohada
2020-08-08 17:47           ` Sungjong Seo
2020-08-12  9:19             ` Tetsuhiro Kohada
2020-08-13  4:03               ` Namjae Jeon [this message]
2020-08-18  1:20                 ` Tetsuhiro Kohada
2020-06-16  6:16 Markus Elfring
2020-06-16 14:45 ` Matthew Wilcox

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