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Compression and Last Accessed dates


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#1 Zeromus-X

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Posted 20 September 2012 - 09:25 PM

I tried doing a bit of searching, but this one seems to be a new one here.

If I'm running an NTFS-formatted Windows XP Home system (i.e. no audit trail enabled, as that's a Pro-only feature), and a drive is compressed, would this compression change the "last accessed" date of the files it is compressing? Technically, it has to access the files in order to compress them, so it'd seem to make sense. I don't have a spare drive here to test this with, so I figured maybe someone here would know.

If this is the wrong forum for such an off-the-wall question, please move accordingly. Thanks!

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#2 Baltboy

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Posted 21 September 2012 - 10:37 AM

After the initial compression of the drive compression and decompression only takes place when you access the file so the access date should be the same. Also keep in mind when using compression the file must be decompressed before using it. You must retain enough free space on the drive to use it uncompressed which limits the amount of space you actually save using compression. Also as a final though compression puts a big performance hit on read and write times. With the relatively inexpensive storage media available using compression on anything other than backups IMHO isn't worth the performance hit.
Get your facts first, then you can distort them as you please.
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#3 Zeromus-X

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Posted 21 September 2012 - 11:39 AM

I'm well aware of the performance hit. This is for a business client of mine who is trying to find out if some files were accessed by a (former) employee. Problem is, their backup device is smaller than their combined systems will allow, so they're compressing the entire volume onto the backup device (compression then copy, not copy then compress). My problem is that I don't want to dig into this if the compression will have altered the file modified and/or file access dates, and I'd rather just tell them "can't do it" than tear apart their hardware and cost them a bunch of money.

Since by nature compression involves opening up the contents of a file (not in an executable format but the file itself must still be opened to see the data it contains), modifying them (via compression), and then storing the file in a compressed format, logic would tell me that this would HAVE to affect the modified and accessed dates. One could even argue that the compressed result is a new file, thus changing the "create" date, though I can't imagine that's happening. If compression of a file affects its modified and accessed dates, and there's no audit trail in XP Home, that means we can't find what we're looking for. On the flip side, if compression does NOT affect those things, it makes me wonder what other changes can be made to a file without affecting them.

#4 noknojon

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Posted 21 September 2012 - 06:09 PM

and I'd rather just tell them "can't do it" than tear apart their hardware and cost them a bunch of money.

I think you just answered your own question in the above statement !!!!!!!!!!
Tell them it will cost more than it is worth for a minor job like they want, or make a big profit and do the job slowly -

#5 Baltboy

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Posted 23 September 2012 - 02:26 PM

The act of compression itself will not modify the accessed, created, or modified dates. Those attributes will remain the same since those dates are only modified during User access. However since the files are being then being backed up onto the external drive hence created as new files then the all of the dates should have been reset since the date of the backup will become the date of creation on the backup media. The attributes of the files listed on the source drive should remain unchanged regardless of compression or backup.
Get your facts first, then you can distort them as you please.
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#6 Zeromus-X

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Posted 24 September 2012 - 09:46 PM

Got it. So file manipulation by another program won't necessarily impact the access date, but any possible manipulation by a person will. Hmm.

Thanks for the quick answers.




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