What's the best Filesystem?

Discussions related to using VirtualBox on Windows hosts.

What's the best Filesystem?

Postby JohnoPolo » 29. Apr 2013, 14:51

Hello. On a Windows 7 64 bit virtual machine I have developed a VDI: Invalid Header and having spent several hours scouring the forums (and elsewhere), it seems like my data is toast. I also read about "don't use VDI" and "Avoid using VHD files in VirtualBox" - so what should I use? Help and advice would be appreciated but kindly note that I'm just an ordinary user trying to make use of VirtualBox and I don't want to become an expert in ... anything :-)
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Re: What's the best Filesystem?

Postby mpack » 29. Apr 2013, 14:56

Where did you see any message about avoiding VDI? VDI is the native container format in VirtualBox and should be used when possible. Any file on your PC can be corrupted, but VHD corruption is more likely. The best cure is a three step strategy: (1) use VDI, (2) avoid snapshots (people who use them are more likely to run out of host disk space), (3) make proper backups.

I don't recognize your "VDI: Invalid header" message. In what context do you see this error, and where did you get the VDI which it refers to?
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Re: What's the best Filesystem?

Postby JohnoPolo » 29. Apr 2013, 15:28

I get an error when I try to access the virtual machine:

Failed to open a session for the virtual machine Tor Browsing & Vuze.
No error info.
Result Code: E_FAIL (0x80004005)
Component: ProgressProxy
Interface: IProgress {c20238e4-3221-4d3f-8891-81ce92d9f913}


The attached image details the header issue.
Attachments
VirtualBox error1 (Medium).jpg
VirtualBox error1 (Medium).jpg (66.99 KiB) Viewed 478 times
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Re: What's the best Filesystem?

Postby mpack » 29. Apr 2013, 16:19

I see. In that case I expect the error message means what it says: that VDI is corrupted, truncated etc. Without further information I couldn't tell you why (*), but it probably doesn't matter - I see that it's a clone, so presumably you can make another copy of the original.

(*) A typical mistake would be transporting these files on a FAT formatted removable drive, not noticing that FAT truncates the file at 4GB.
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Re: What's the best Filesystem?

Postby JohnoPolo » 29. Apr 2013, 17:19

Thanks for all the input. As for what caused the error, it certainly wasn't due to "moving" the file: that resides on a 1TB fixed hard drive and hasn't been touched since it was created. However, the physical drive (D: in this case) was running short of space and had only about 50GB available. This I discovered after the error occurred and after reading something somewhere (I really can't recall - and it might even have been about VHD files) to the effect that running short of space on the host drive can corrupt VIrtualBox files.

The "clone" was made so that I could replicate the OS but thereafter the .vdi file got a life all of its own. Sadly I don't have a backup but there wasn't anything there that can't be recreated - albeit with some considerable schlep. My confidence in VirtualBox is somewhat diminished though and perhaps I should look at alternatives. Any suggestions or advice would be appreciated.
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Re: What's the best Filesystem?

Postby mpack » 29. Apr 2013, 17:24

The design of VHD makes it subject to corruption when the host runs out of disk space. But, I don't know why that should reduce your confidence in VirtualBox, since VHD was not designed or recommended by the VBox devteam, they merely added support for people like you who make their choice to use that format. VDI was designed by the VBox devteam, and has no such problem.

As I said earlier, without knowing the cause or nature of your data corruption I'm not really in a position to speculate about it. I can tell you that no-one else has reported a similar problem that I can recall.
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Re: What's the best Filesystem?

Postby JohnoPolo » 29. Apr 2013, 17:40

My loss of confidence hasn't anything to do with VHD files (I don't use them) but it has everything to do with having a .vdi file that has become unreadable for no apparent reason - and I think it's fair to suggest that this malfunction could well happen again. Let me add that the host machine continues to purr along nicely and all the other contents of drive D: are accessible.
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Re: What's the best Filesystem?

Postby mpack » 29. Apr 2013, 17:45

JohnoPolo wrote:I think it's fair to suggest that this malfunction could well happen again

Quite so, but I'm only curious about why you immediately assumed that the fault was with VirtualBox, when nobody else has reported similar issues.

How did you make these clones? The file naming suggests CloneVDI, except I know that all but the most ancient versions of CloneVDI have quite accurate size estimates for the clone, and give advance warning if disk space is too low, in addition to an error dialog when disk space actually runs out.
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Re: What's the best Filesystem?

Postby JohnoPolo » 29. Apr 2013, 19:09

I did indeed use CloneVDI version 2.5.0.0 and I recall allocating 100GB to the .vdi file. As for what went wrong, I can of course only "eliminate possibilities" based on what's still working:
1. The host is normal.
2. The three other virtual machines are normal.
3. I haven't altered or added any software to the damaged machine (which is in daily use) in months.
What's left that could have gone wrong?
Is there any chance of recreating the .vdi header - or of extracting the data?
(It's past midnight where I am so I'm off to bed :-)
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Re: What's the best Filesystem?

Postby mpack » 29. Apr 2013, 20:36

I can't answer your question about the chances of extracting the data: that would depend on the nature of the corruption, and I have no way to know that. In the past when something similar happened, the user had tried to edit the document with an inappropriate tool, causing the first 64 bytes of data to be zeroed. In VDI that area happens to be static - so replacing that data with a patch tool repaired the file.

If you examine the clones with CloneVDI, does it agree that they are corrupt?

Perhaps it would be worth your while to view the first few hundred bytes of the file in a hex editor such as frHed, and post a picture of the result here. That way we can see how much of the header is left.
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Re: What's the best Filesystem?

Postby JohnoPolo » 30. Apr 2013, 03:10

Now that I've happened upon who I'm dealing with here, I'm pleased to know that I couldn't be in better hands. Thanks for your time :-)
1. I tried to re-clone the damaged file but that didn't work.
CloneVDI.jpg
CloneVDI.jpg (93.08 KiB) Viewed 435 times

2. I extracted the first 100K of the .vdi file and saved it as ".zip" (I couldn't upload it without an extension and .txt didn't preserve the data)
Attachments
Clone of Win 7 dump 1st 100K.vdi.zip
(23.75 KiB) Downloaded 4 times
Last edited by mpack on 30. Apr 2013, 11:31, edited 1 time in total.
Reason: Correct misleading attachment name.
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Re: What's the best Filesystem?

Postby mpack » 30. Apr 2013, 10:56

That was confusing. I thought you were giving me an actual zip file, not just renaming the extension on a raw binary. I will investigate what the error means.

[Edit] I replaced your pseudo-zip with an actual zip to avoid further confusion plus save space.
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Re: What's the best Filesystem?

Postby mpack » 30. Apr 2013, 11:29

Ok, I've had a look, and the bad news is that this VDI header is comprehensively trashed. The preheader (static first 72 bytes) is ok, then the first dozen bytes or so of the true header is also ok, but once we get into the disk size and block size fields, its all garbage, right to the end of the first sector (512 bytes). It looks like the block map in the second sector might be ok, but that's just a guess based on the regular looking ascending pattern - which looks like a block map should.

I suspect that if you knew what you were doing, e.g. if you knew the correct values for the disk size fields, then you could repair this with the hex editor. The most vital structure is the block map - if that is garbage then the disk is lost, but it does look probably ok.

Did you do something unusual to the file that might have caused this corruption? E.g. edit it, try to patch it, copy it on media with bad sectors etc? If you know what you did, and still have the copy from before you did it, then you can recover the drive that way.
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Re: What's the best Filesystem?

Postby JohnoPolo » 30. Apr 2013, 12:13

Like I said before, I didn't do anything to the file. The virtual machine was running (only this one) as it normally did: a few tabs in Firefox were open (only one instance) and Vuze was busy downloading a couple of torrents. I first noticed something amiss when Vuse became non-responsive. Everything was still on the screen but nothing was happening. I powered off the VM and then restarted it. It booted up normally and loaded Vuze and then the screen went west - perhaps a red background - I can't recall exactly. Whatever, the machine stopped responding. I shut down the virtual machine and then shut down the PC. When I restarted the VM, I got the error. The data from Vuze was being stored in a shared folder which I can access from another VM and that all looks okay.
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Re: What's the best Filesystem?

Postby mpack » 30. Apr 2013, 13:19

Please clarify if the other VDIs I see in the first posted picture are readable? And was the (browsingcopy) clone a straight clone with no resize?

If yes to both then you might get success by copying the first 512 bytes from the old VDI to the new using the hex editor (obviously, make a backup first). That would give you a valid VDI with UUID fields that clash with the old file, so clone with CloneVDI to cure the latter and that should (may) get your disk back, which you can then build a new VM around.

Also, given your description of what happened, I would run a disk check on your host.
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