Windows Thread, Single Instance Storage and restoring shadow copies in Technical; I'm eyeing this up for the space-saving feature, more than anything. One copy of $large_reference_doc, rather than 300 across different ...
20th February 2008, 02:49 PM #1
Single Instance Storage and restoring shadow copies
I'm eyeing this up for the space-saving feature, more than anything. One copy of $large_reference_doc, rather than 300 across different homedirs would be handy.
But I'm not entirely sure how it works with shadow copies. I've read:
But what happens if someone with the original version accidentally deletes his link in his home directory and then tries to restore if from shadow copy / previous versions tab? Would he get the original or revised version back?
Two users receive the same e-mail with an attachment. They both save the attachment to their home folder. SIS runs in the background and detects the two identical files on the volume and moves one of the copies into the SIS common store and replaces both files with a pointer to the file in the SIS common store.
One of the users makes a change to the file. SIS immediately detects that an update is pending for the file removes the pointer in the users home folder and replaces it with a copy of the file in the SIS common store. The updates are then applied to a fresh copy of the original file. This is completely transparent to the application.
The other user's file remains in the SIS common store with a pointer in the user's home folder, even if there is only one pointer to the file. When the second user updates the file (assuming there are no other pointers) the pointer is deleted and replaced with a copy of the original file and the file in the SIS common store is deleted.
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20th February 2008, 03:24 PM #2
It sounds just like a unix hardlink, if thats correct then deleting the 'file' will only delete the link, the original node will stay intact. restoring the file would copy the file, rather than the hardlink (unless you restore the link). I'm guessing here as I don't have direct experience of how windows does this.
20th February 2008, 03:48 PM #3
Reading the docs, it uses a groveller function similar to RIS, via a driver, but I'm unsure (and the tech overviews I've found so far don't mention) how it works with shadow copy restore in the above situation.
If there's no link to the original file in anyone's homedir, there's no reason for the groveller to maintain the central copy and I'm wondering what shadow copy does in that situation and whether a restore would relink the file to the user homedir or not.
Last edited by pete; 20th February 2008 at 04:10 PM.
20th February 2008, 06:22 PM #4
My, somewhat limited, understaning of it is that: Person A & B recieve attachment via email. Both save to home dirs. System realises that they are the same, copies to SIS common store, we'll call it file(A). Person B edits file and saves it. SIS store realises copies the original file to their home dir and saves it. We'll call it file(B). the original file "file(A)" remains in the SIS store. In your scenario, Person A deletes their (link to) file(A), realises and restores via shadow copies. Because (so i understand) they restore the link (which is in their home dir), it would be file(A) that they see when they open it. I know what you mean about it being cleaned up as no links remain but if it is compatible with shadow copies then that is a seperate copy of it.
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