Time Machine over network... some thoughts

[jmmo20]

After enabling Time Machine over the network (Airdisk) I realise that one of the issues that will most certainly lead to backup data loss is sparsebundle management.

Basically, Time Machines creates a .sparsebundle on the destination volume (airdisk or whatever..).
once Time Machine is about to backup or restore, it mounts the network volume and also the sparsebundle volume within it.

Now, if the network conection drops, the whole sparse bundle gets corrupted and all data is lost. It doesn't happen often (in fact I use .Mac Backup over airdisk and the same thing could happen but never has).

Another thing is that Time Machine does not unmount the sparsebundle once it finishes using it. It is a problem if you forget and don't unmount it manually. You could put your mac to sleep while the sparsebundle is mounted. I've been doing test with dummy sparsebundles and this leads to corruption about 50% of the time.

Apple could easily fix the latter by ensuring the sparsebundle volume is correctly unmounted upon completion.

The former I'm not so sure.. I don't like the idea of using sparsebundles in the first place (like I don't like the ideas of sparseimages for FileVault.. a simple Kernel panic leads to corruption of all data.).

How did Time Machine over Airdisk work in the betas? Was it through a sparsebundle or writing directly onto the airdisk volume?

 

[pkulak]

I found this after doing a Google search, and I thought I'd bump it just because the parent brings up a lot of good points. If sparse bundles really are that fragile, that could be a huge issue. I would think, however, that the reason there are so many "bands" is just so that if one gets corrupted you only loose the files overlapping that band.

 

[/dev/toaster]

These are the reasons I suspect Apple pulled the plug before release. The images get corrupt far too easy. There is no protections in place and to top things off, there are no repair utilities.

In the developer seeds, it worked the same way ... by creating an image on the target NAS. It did the same thing on AFP and SMB. (I heard it being done on NFS, but I personally didn't try)

My question is, why did they close off SMB and AFP (plus airdisk) but allow it for a remote Leopard machine. I did some basic tests with this, but since I have 2 laptops it wasn't the best of tests. Has anyone tried this ? Are the same problems present regarding corrupt images ?

I fear that Apple might not come up with a solution to it. I would have expected a fix to be present in 10.5.1.

 

[Mindflux]

Another thing is that Time Machine does not unmount the sparsebundle once it finishes using it. It is a problem if you forget and don't unmount it manually. You could put your mac to sleep while the sparsebundle is mounted. I've been doing test with dummy sparsebundles and this leads to corruption about 50% of the time.

Uh, yes it does. every time Time Machine launches for me I get a mount icon on my desktop and when it completes Time Machine unmounts the drive (and the icon disappears).

I can see having service interruptions corrupt the sparse bundle as a problem. Probably part of the reason they removed the airdisk support along with the changes to the AFP protocol.

 

[Mindflux]

My question is, why did they close off SMB and AFP (plus airdisk) but allow it for a remote Leopard machine. I did some basic tests with this, but since I have 2 laptops it wasn't the best of tests. Has anyone tried this ? Are the same problems present regarding corrupt images ?

I read there were changes to the AFP protocol in Leopard, which explains why backing up to another Leopard share is supported. It had to do with actually checking to make sure the data was there and intact. (Probably some sort of hash check).

 

[GoodWatch]

The whole point about making back-ups is that they must provide a fall-back in case of an emergency. That means that not only Time Machine must be able to use networked drives, in this case networked drives over a wireless connection, but must also contain an algorithm that checks if blocks of data are written on the target without errors and do a retry if they aren’t to maintain integrity. Far and beyond what IP does. I have chosen to connect a 500 GB FireWire drive directly to my iMac and use the AirDrive for other purposes. It’s much faster anyway.

 

[/dev/toaster]

Uh, yes it does. every time Time Machine launches for me I get a mount icon on my desktop and when it completes Time Machine unmounts the drive (and the icon disappears).

I can see having service interruptions corrupt the sparse bundle as a problem. Probably part of the reason they removed the airdisk support along with the changes to the AFP protocol.

Interesting, because it does not unmount for me ... on 2 different machines. I am doing it over SMB presently.

 

[/dev/toaster]

I read there were changes to the AFP protocol in Leopard, which explains why backing up to another Leopard share is supported. It had to do with actually checking to make sure the data was there and intact. (Probably some sort of hash check).

I can see this being the case ... however, has anyone tested how well it works ?

 

[Mindflux]

Interesting, because it does not unmount for me ... on 2 different machines. I am doing it over SMB presently.

My air disk is mounted over AFP. Shrug.

 

[pkulak]

Interesting, because it does not unmount for me ... on 2 different machines. I am doing it over SMB presently.

Yeah, SMB is your problem. I used to use SMB, but I've noticed that AFP (Netatalk) works a lot better. The client machines are able to auto mount shares and, apparently, auto unmount. I would suggest running Netatalk as well.

 

[Coolnat2004]

Yeah, SMB is your problem. I used to use SMB, but I've noticed that AFP (Netatalk) works a lot better. The client machines are able to auto mount shares and, apparently, auto unmount. I would suggest running Netatalk as well.

I am using SMB, and it unmounts properly.

 

[/dev/toaster]

Yeah, SMB is your problem. I used to use SMB, but I've noticed that AFP (Netatalk) works a lot better. The client machines are able to auto mount shares and, apparently, auto unmount. I would suggest running Netatalk as well.

Thats actually what I want. I have not been able to get netatalk to work on my Linux box, which is why I am running Samba. I would rather AFP, since its so much faster.

Can you send me a copy of your config ?

 

[pilotError]

I've been using TM to my ReadyNAS NV+ over AFP (over wireless G) for the last week now.

I've been playing with restores and haven't had any issues to date, even with my iMac sleeping during the day. Mine doesn't dismount.

I also don't re-mount anything. I have manually ejected the drive, and TM sees the share and re-mounts it to do the backup.

The only issue I have is when I want to go back in time, I have to right click TM on the dock and browse other time Machine disks. Once I select the disk, it works great. In fact, I installed iWork 08 today and removed iWork 06 demo. I went back to earlier today and did a restore of iWork 06 and it worked pretty quickly even over wireless.

I've gone back and brought back desktop items, so I know its working. Hopefully this thing doesn't go south on me!

Let's hope 10.5.1 fixes the issue.

 

[pkulak]

Thats actually what I want. I have not been able to get netatalk to work on my Linux box, which is why I am running Samba. I would rather AFP, since its so much faster.

Can you send me a copy of your config ?

I'm running Ubuntu and all I did was follow some tutorial on the web for setting it up with encryption. I didn't change my config except for adding an .AppleVolumes file in my home directory to add my external HD as a separate Time Machine share.

 

[/dev/toaster]

Do you have a link ? I have tried a number of suggestions, but found none that work. Did you compile it custom ?

If Apple fixes Airdisks then that will work for me. They seem to have many problems as well.

Has anyone found a way to repair corrupt images without re-creating them ?