Converting normal drive to writethrough drive

[lnoland]

I created a large (2TB) fixed-size VDI for holding videos recorded with mythtv. I thought I had created it writethrough but apparently I did not. By the time I realized my error I had over 900GB of data stored in a differencing disk. I would like to change the drive to writethrough but I"m not sure how to do it. As I understand I have to remove it from the VM in order to do that but that would mean that I would have to merge the differencing disk first. I'm reluctant to do that because I have two snapshots (let's call the earliest 1 and the latest 2) and previous attempts to delete (merge) snapshot 1 have always ended in an error. I'm a bit afraid of what might happen if I merge snapshot 2 since it appears that there might be something wrong with snapshot 1. I created the disk after snapshot 1 was taken so it only has one differencing image -- is it possible to merge just the one disk and leave the system disk alone?

If merging everything is my only option, I could use some brainstorming ideas for other approaches. I thought about just creating another disk and copying all the data (very slowly) to it but I don't have enough disk space to create another 2TB disk.

Thanks for any help you can offer.

[mpack]

Why on earth did you make it fixed size? That decision is at the root of all of your subsequent problems. That and the decision to use snapshots, and I'll bet with a fixed drive of that size then backups are out of the question too.

If it was me, I'd first use CloneVDI to clone the latest snapshot of the humungous drive: cloning to an external drive since I assume space will be a problem anywhere else. I'm afraid that means the process will be slow. Then I'd detach that drive from the VM then clone the VM to get rid of the remaining snapshots. Then you can attach the cloned secondary VDI and do what you like with it: however writethough only makes sense if you continue using snapshots, and I'm curious to know why you did that too.

[lnoland]

Why on earth did you make it fixed size? That decision is at the root of all of your subsequent problems. That and the decision to use snapshots, and I'll bet with a fixed drive of that size then backups are out of the question too.

If it was me, I'd first use CloneVDI to clone the latest snapshot of the humungous drive: cloning to an external drive since I assume space will be a problem anywhere else. I'm afraid that means the process will be slow. Then I'd detach that drive from the VM then clone the VM to get rid of the remaining snapshots. Then you can attach the cloned secondary VDI and do what you like with it: however writethough only makes sense if you continue using snapshots, and I'm curious to know why you did that too.

Thanks for the reply. To satisfy your curiosity -- I made it a fixed-size disk because I had been told that a dynamic disk could cause delays which could cause problems with video-recording. Of course, I suspect that the differencing disk could cause similar problems but then, it wasn't my plan to have a differencing disk. As for snapshots, I intended to use snapshots as a substitute for backups since I have never been able to find a bare-metal backup program for Linux which doesn't come with a $1000+/year price tag. Of course once I encountered the problem deleting my oldest snapshot I started to question whether there was enough reliability there to count on for backup purposes. As for the writethrough disks, they were intended to hold only videos which are never backed up -- while it would be nice to have enough disk space to keep backups of all my videos, it would be rather expensive and unwieldy and, ultimately, while I don't wish to lose them, they are an unnecessary extravagance so if a disk failure destroyed them, I would be unhappy but not devastated.

Thanks for your suggestions -- as I indicated, I don't currently have enough disk space to clone the drive so, I will either have to find an alternative or wait until I can afford more disk space. But I appreciate your suggestions.

[scottgus1]

Snapshots make a guest more delicate and do not work as backups. They can be considered similar to Windows' System Restore points: point-in-past-time markers, not extractable, useless without the base system in place, but easier to corrupt because the files are accessible. They should only be used on guests you're experimenting with and with data you wouldn't mind losing. (The forums are replete with users destroying their important data because they did something wrong with a snapshot.)

I have a movie server at home. It does not store the data via Virtualbox, but considering the backup structure might be useful. It has four 2TB drives (internal or external averaging $100 on Newegg, BTW). 2 drives, 4TB, carry movies & other data, the other two are Robocopy-generated copy-only-no-delete mirrors of the first two. I also have two external 2TB drives for each 2TB drive set, one set kept at home, one set kept at work, and I rotate them. Every so often I run a WinMerge on the main drives, mirrors, and externals, to check backup integrity. Only thing that will delete my data is a nuclear war. Were I to use Virtualbox to store recorded videos I would still make backups, perhaps via copying the recordings to shared folders or some such, perhaps by copying the VDI's.