backing up with rsync and extended attributes

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backing up with rsync and extended attributes

I'm currently using rsync to backup my home directory to an external drive connected to my Airport Extreme Base Station and the hard drive is formatted as HFS+.

Do I still have to use the -E flag to preserve extended attributes if I am backing it up to the drive formatted and connected in this way? My thinking is that, since it is mounted in Leopard and formatted as HFS+, the OS is making sure that the files exist with the necessary resource fork or extended attribute information. I'd like to not use -E because it copies the ._. files on my machine every time and this adds tremendously to the time it takes to backup the data but I don't want to compromise data integrity.

Any help would be great. Thanks!

Macbook Pro 2.2 GHz, Mac OS X (10.5.2)

Posted on Mar 4, 2008 11:46 AM

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Answer 1

Mar 4, 2008 11:57 AM in response to Idris33

Idris33,

Yes, you still need to use the "-E" option. I have to ask, though: Are you using the -a option? This option, the "archive" option, will cause rsync to operate in "incremental mode," where only those files that are new or have changed will be backed up. This is the preferred option, and it will save a great deal of time when making backups.

Scott

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Answer 2

Idris33 Author

Level 1

5 points

Mar 4, 2008 12:02 PM in response to Scott Radloff

Thanks Scott!

Yes, I use the -avE flags when backing up. The only problem is that it copies all of the ._. files every time. I was hoping that I could get away with only having -av to make it shorter.

Do you know what problems I may have if I only use -av ? Will this result in loss of data? I've seen a couple of Mac websites that demonstrate rsync scripts without -E and I don't know if this results in a loss of data when attempting to restore a file from backup. I don't backup apps or system info, I only backup my home directory.

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Answer 3

Mar 4, 2008 1:04 PM in response to Idris33

Resource files don't have a modtime, so the rsync that comes with OSX copies ALL resource files. Yes, you may lose stuff without the -E option, but normally only "metadata", such as application associations, etc. many people use rsync with Linux servers without backing up resource files, since they are expendable anyway.

Read here for more.

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Answer 4

Mar 4, 2008 2:06 PM in response to Idris33

Idris33,

It really depends on what you are backing up. For almost every file, it won't matter whether the resource fork is being copied. If I use rsync, however, I must use the -E option, because I make heavy use of "text clippings" for some things, and text clippings are useless without the resource fork.

If you are making a backup of a given HOME folder with the intention that it be a completely restorable and portable "environment," as I do, resource forks will be mandatory. If, on the other hand, you simply want to back up the majority of your files (with the exception of those entirely dependent on resource forks, such as the aforementioned text clippings), rsync can be used without the -E option.

One thing that puzzles me, though, is why this is an issue with your configuration. I don't use the Airport Extreme to share a network drive, but it would seem to me that an HFS+ volume, being shared over the network, would accept data without "splitting" the resource fork. Does the AE only share a drive over the network using SMB (which would explain this phenomenon), or is it possible that you are mounting it via SMB by choice? If possible, can you mount the drive via AFP?

Scott

Scott

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Answer 5

Idris33 Author

Level 1

5 points

Mar 5, 2008 7:28 AM in response to Scott Radloff

Scott,

I think that what you're puzzled about is the same thing that I'm puzzled about. My assumption is that I would need the -E flag only if I was backing up to a different (non-Mac) server or to an external drive that is a FAT or other non-Mac volume. But since this is an external drive (an HFS+ volume) attached via USB to an AEBS, then I thought that maybe rsync wont need the -E flag and I can save some time and wireless bandwidth by dropping -E and the Macs that I'm backing up.

I'm not mounting it via SMB, I'm mounting it via AFP as far as I know. I think this because I attempted to make an Automator action to connect to it. Automator detected it and only gave me the option of mounting it via AFP so I'm assuming that that is how it is being mounted when the system does it.

Thanks!

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