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We have two qnap devices - one in our datacentre and one off-site. We have hundreds of password protected RAR files stored on the qnap that contain virtual machine image snapshots, with approx 20 of them being created each day.

We synchronise the two devices using rsync, and it looks like all the files are being rsynced OK - they come over and have the same file size and all the files are present and accounted for.

However, when I try to open the RAR files on the remote site, I get

Cannot open \\qnap01\FromDatacentre\Snapshots\DB001SQL1-20110626.rar

I can open the RAR files on the local site just fine, so I assume that something is getting mangled during the rsync procedure. However, the older files (pre 2011-06-20) work just fine, it's something that's only started happening in the last week.

There haven't been (as far as I know) any changes to any of the devices, setup or configuration in that time. Obviously something has changed though.

Where should I start investigating?

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up vote 3 down vote accepted

Can you open other files on the offsite qnap?

You might pick a smallish file, or set of files and run md5sum against them on each qnap to make sure the files are the same. (If the md5sums of both files are the same, the files are identical)

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Yeah, other files on the offsite qnap are fine - it's just these rsync'd files. We actually have files being rsync'd in the opposite direction and those files are OK. I'll do an MD5SUM on them now (they're all pretty big files though, so I was hoping to avoid, but I dont think I have a choice) – Mark Henderson Jun 27 '11 at 23:50
Thanks - this pointed me in the right direction. Turns out that something is mangling the permissions on the file, but I think that's a Windows issue, not a qnap issue. – Mark Henderson Jun 27 '11 at 23:57

Giving Jodie the checkmark as s/he pointed me in the right direction, but it turns out that the issue is related to the fact that the two qnap devices belonged to different active directory domains, and someone had gone and turned on "advanced file permissions" on the local site.

This meant that qnap was managing the ACLs itself, rather than letting Windows do it, and when the files were being rsynced the ACLs were coming with it and being locked by the remote qnap, but the remote qnap, because it belonged to a different active directory domain, didn't have any matching SIDs.

I turned on Advanced File Permissions on the remote qnap and told it to replace all ACLs on the destination folders with valid ACLs for the remote site and now everything came good.

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