Messages in this thread | | | Date | Tue, 21 Mar 2006 21:05:13 +0100 | From | Pavel Machek <> | Subject | Re: Question regarding to store file system metadata in database |
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Hi!
> Second, I might want to give the background on which we are > considering the possibility of storing metadata in database. We are > currently developing a file system that allows multiple virtual > machines to share base software environment. With our current design, > a new VM can be deployed in several seconds by inheriting the file > system of an existing VM. If a VM is to modify a shared file, the file > system will do copy-on-write to gernerate a private copy for this VM. > Thus, there could be multiple physical copies for a virtual pathname. > Even more complicated, a physical copy could be shared by arbitrary > subset of VMs. Now let's consider how to support this using regular > file system. You can treat VMs as clients or users of a standard > linux. Consider the following scenario: VM2 inherit VM1's file > system. The physical copy for virtual file F is F.1. Then, it modified > file F and get its private copy F.2. Now VM3 inherit VM2's file > system. The inherit graph is as follow: > VM1-->VM2-->VM3 > > Now VM3 wants to access virtual file F. It has to determine the right > physical copy. The right answer is F.2. But in the file system, we > have F.1 and F.2. So some mapping mechanism must be devised. No matter > how we manipulate the pathname of physical copies, several disk > accesses seem to be required for a mapping operation. That is the > reason we are considering database to store metadata.
Hardlinks? ext3cow (google it)? Pavel
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