Everything backed up - daylight savings/British Summer time effect?

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jim

06 Apr, 2012 03:03 PM

I store all my photos and music files (500GB) on an external drive, and back them up with CCC to a second external drive. This usually works OK, and is quick, as most of the files do not change. However, I recently took a lot of photos, and after editing and cataloguing with Lightroom I went to back them up. To my horror, every file was first backed up into the CCC archive folder, which took ages and used up a lot of my backup drive. The new files backed up OK, and when I examined the system I found that the source files and the backup files seemed identical (creation date, modification date, file size etc). However, the newly backed up files in the CCC archive folder all had Creation Date, Modified and Last opened dates exactly 1 hour later than the source or backup files. I assume this must be something to do with the fact that we (in Britain) recently put our clocks (including computer clocks) forward 1 hour for Summer.

Assuming you know the answer(s), please can you tell me how to prevent this happening again, and how can I recover the 500GB of needlessly used space on my backup drive (the archive files) without messing up CCC's housekeeping. Many thanks for any help you can give. - Jim Leppard

  1. Support Staff 2 Posted by Mike Bombich on 06 Apr, 2012 03:41 PM

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    Hi Jim:

    We change our clocks too, but that shouldn't affect the actual modification date of the file, only the presentation of the date in the Finder. The modification date that is recorded on disk is based on GMT (well, probably UTC). If it wasn't, people would have all kinds of problems with more regular changes, like traveling from one time zone to another (which is fairly common in the US anyway). But you can change the Time Zone setting all day long, even in the middle of a backup task and it won't affect the modification dates. I just did a quick test to verify this. I copied some data to a disk, changed the time zone, and re-ran the backup and nothing was recopied. I actually ran this several times, making lots of changes to the date (including setting the date back to early March, and then back again), and each time nothing was recopied.

    With my understanding of how the modification date for a file is stored on disk, I'm struggling to explain what happened here. I honestly have no idea. I'm stating the obvious here, but the oddity is that the modification date of the files in the _CCC Archives folder (e.g. the stuff that was previously backed up from the same source) is different from the source.

    Under the assumption that you backed up the same source volume to the same destination volume prior to the DST switch, and that the disk was not attached to any other computers between the last backup and this current backup, the only way that I can explain the difference is that the actual modification dates on those files were either changed on the source or on the destination.

    Mike

  2. 3 Posted by Jim Leppard on 06 Apr, 2012 04:43 PM

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    Thank you for this Mike - it confirms my understanding of how things *should* happen, without telling me how to avoid it happening again. I guess I'll have to hope for the best, and to this end I repeated the backup immediately after the first one: nothing at all was copied, which was what I had hoped for (and expected).

    So, hoping all is well for the future, please can you tell me how best to go about recovering the 500GB of -CCC archive space (with the faulty dates on the files)?

    Many thanks for the quick response last time.

    Jim

    PS File dates on source and backup were as I expected, and, to confirm, the _CCC archive folder file dates were 1 hour greater than the source and backup: I don't see how the source and backup file dates could have been changed.

    On 6 Apr 2012, at 16:41, Mike Bombich wrote:

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  3. Support Staff 4 Posted by Mike Bombich on 06 Apr, 2012 06:10 PM

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    Hi Jim:

    can you tell me how best to go about recovering the 500GB of -CCC archive space (with the faulty dates on the files)?

    Just drag the folder to the Trash and empty the Trash.

    Mike

  4. 5 Posted by Jim Leppard on 07 Apr, 2012 01:36 AM

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    Many thanks - I didn't like to risk it without advice, in case CCC keeps track in some way of where things are.

    Jim

    On 6 Apr 2012, at 19:10, Mike Bombich wrote:

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  5. 6 Posted by Jim Leppard on 07 Apr, 2012 04:51 PM

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    I removed the offending archive folders and tried the backup again. It worked perfectly, so it looks like the problem has gone away (for now). I still have no idea what caused it though :-( Anyway, thanks for all your help and guidance. - Jim

    On 6 Apr 2012, at 19:10, Mike Bombich wrote:

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  6. 7 Posted by Denis Russell on 25 Apr, 2012 01:54 PM

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    I've just suffered what looks to be the same problem and came looking for a solution. First my setup:

    I'm using CCC to back up flash cards from my camera onto my Mac. The plan was that whenever I put the flash card in CCC copies anything new to my backup file. This allows me to keep some old photos on my camera to view via the screen, but delete them when I need space, knowing I have a full set courtesy of CCC. Problem is that it has just done what Jim described - moved GBs of old stuff into an archive file and copied all of the multi-GB flash card into new files. When I look, the problem would appear to be that the archived files have times +1 hr.

    I don't seem to get the same problem when backing up from my mac to an external hard drive (thank goodness!!!).

    I think I ran into the same problem last Autumn/Fall. At the time, I thought I'd been playing with photoinfo and blamed myself, but that is definitely not the case this time.

    I understand Mike's comments about storing times in UT in general terms, and that is what I would have expected. Not knowing the details, I wonder if it has something to do with the very simple filing system used on flash cards, and some subtle difference between the handling of dates on Mac OS Extended and FAT 32?

      Denis
    
  7. Support Staff 8 Posted by Mike Bombich on 26 Apr, 2012 02:38 AM

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    Hi Denis:

    I would actually expect to see this problem with a FAT32 destination. Modern filesystems store dates (creation, modification, access) relative to UTC, but FAT stores them relative to the computer's local time. So if you eject the FAT32 volume, change the time zone, then reattach the FAT32 volume, the file modification times will all be off by the time zone difference.

    I never asked Jim whether his destination was an HFS+ volume, I probably should not have assumed that. If it's a FAT32 volume, then this explains the problem precisely.

    Microsoft describes this matter fairly clearly here:

    http://msdn.microsoft.com/en-us/library/ms724290(VS.85).aspx

    I think this is worth mentioning in the documentation as well.

    ...

    http://help.bombich.com/kb/usage-scenarios/backing-up-tofrom-networ...

    Mike

  8. 9 Posted by Denis Russell on 26 Apr, 2012 09:07 AM

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    Many thanks, Mike. At least that explains what the cause of my problem is. It might be worth CCC giving a warning if it detects a FAT32 volume???

    Now I need to think if I can somehow manage to retrieve the behaviour that I wanted even across the switch to and from daylight saving. First I need to read carefully the stuff you referred to.

    Thanks again for a great program.

    Denis

    On 26 Apr 2012, at 03:38, Mike Bombich wrote:

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  9. 10 Posted by Jim Leppard on 26 Apr, 2012 10:24 AM

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    I'm on holiday at present but am pretty sure the source disk was FAT32 and the backup HFS+. Will check when I'm home next week. - Jim

    Sent from my iPhone

    On 26 Apr 2012, at 11:07, "Denis Russell" <[email blocked]> wrote:

    > **** PLEASE REPLY ABOVE THIS LINE ****
    > **** Any part of your response that is below this line will be discarded ****
    > ==================================================
    > From: Denis Russell (Another Carbon Copy Cloner user)
    > Subject: Everything backed up - daylight savings/British Summer time effect?
    >
    > Many thanks, Mike. At least that explains what the cause of my problem is. It might be worth CCC giving a warning if it detects a FAT32 volume???
    >
    > Now I need to think if I can somehow manage to retrieve the behaviour that I wanted even across the switch to and from daylight saving. First I need to read carefully the stuff you referred to.
    >
    > Thanks again for a great program.
    >
    > Denis
    >
    > On 26 Apr 2012, at 03:38, Mike Bombich wrote:
    >
    >> **** PLEASE REPLY ABOVE THIS LINE ****
    >> **** Any part of your response that is below this line will be discarded ****
    >
    >
    > View this discussion at our support site online: http://help.bombich.com/discussions/questions/10592-everything-backed-up-daylight-savingsbritish-summer-time-effect
    >
    >
    >

  10. 11 Posted by Jim Leppard on 01 May, 2012 04:32 PM

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    I'm now back from holiday, and can confirm that my main external storage disk is a USB-connected FAT32, and the backup drive is Firewire + HFS+. Interestingly, when I got back home and tried to backup the 700 or so photo files that I had stored, CCC refused to even start backing them up. I eventually got it to work by ejecting the backup drive and re-connecting it. I see there is an update for CCC now available, which I will install.

    Jim

    On 26 Apr 2012, at 03:37, Mike Bombich wrote:

    > **** PLEASE REPLY ABOVE THIS LINE ****
    > **** Any part of your response that is below this line will be discarded ****

  11. Mike Bombich closed this discussion on 25 May, 2012 09:14 PM.

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