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| Subject: | =?utf-8?Q?Re=3A_tar_incremental_backups_and_ctime=E2=80=8F_probl?= =?utf-8?Q?em?= |
| From: | Vince Rice <vrice AT solidrocksystems DOT com> |
| In-Reply-To: | <CAOKAGPOVnU1Lr2od-UbtRAeZHFKjnNC2jOmmGouVotSYMxbokw@mail.gmail.com> |
| Date: | Mon, 23 May 2016 10:24:07 -0500 |
| Message-Id: | <E0B017A3-43FB-4DCE-AA92-41134EA8D181@solidrocksystems.com> |
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> On Mon, May 23, 2016 at 5:29 PM, Eric Blake <eblake AT redhat DOT com> wrote: >> On 05/23/2016 03:18 AM, x y wrote: >>> It is not clear to me your expectation: >>> - are you asking how to use ctime to select the file with tar alone ? >>> It is not possible for my understanding of the manual. >>> >>> - Are you asking the package maintainer to change the behaviour of >>> cygwin tar ? Unlikely to happen, but I leave to him. >>> >>> >>> Hi Marco, >>> >>> Sorry, I am new to the mailing list. If I am not wrong, tar is >>> checking both of the ctime and mtime values to compare files during >>> incremental backups. Since opening and closing a MS document without >>> changing the content updates ctime, it would be preferable to add a >>> new option to tar to use only mtime for file comparing during >>> incremental backups. >> >> mtime is fakeable, ctime is not. Using only mtime makes it likely that >> your incremental backup will miss files. I don't have any good reason >> to differ from upstream behavior here. > > Hi Eric, > > The problem is not faking time stamps. Even commercial Windows backup > programs are checking the modification time to identify the modified > files. > > Consider that you have a lot of files opened and closed without any > modification in your company. Because of the priority of the ctime > time stamp, reintroducing all of those files to the incremental backup > does not make any sense. tar has also the capacity to create > differential backups with the condition of taking care of the snapshot > file. The ctime issue can result in unnecessarily big differential > backups filled with unmodified files. > > Cygwin tar can be a good alternative for Windows users to do > differential \ incremental backups but the ctime problem must be > solved. This is ultimately Eric’s decision, but… It doesn’t _have_ to be solved. If someone wants to use Cygwin tar as a backup, then that someone lives with the fact that tar uses ctime. The differential might be a little too big, but no actual harm is done. So what. I personally don’t want to have to guess at tar’s behavior. I want to know it’s the same on Cygwin as elsewhere. -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
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