Messages in this thread | | | Date | Thu, 1 Oct 1998 14:37:58 +0100 | From | "Stephen C. Tweedie" <> | Subject | Re: Building Big Ass Linux Machine, what are the limits? |
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Hi,
On Wed, 30 Sep 1998 06:39:40 -0500, Mitchell Blank Jr <mitch@execpc.com> said:
> Redvers Davies wrote: >> Obviously this is completely impractical for some applications (EG: news, >> mailservers etc) - But, in principle, would it be feasable to add this >> functionality into the journalling filesystem ?
> It would be better implemented as a new filesystem that could be layered > atop any other filesystem.
No, you can't really do that efficiently. A true snapshot filesystem needs to be able to take a snapshot of multiple versions of a large database file, where the versions may only differ from each other in a few blocks. That sort of granularity really needs fs support.
> That would also be neat from a managment perspective, since it would > allow you to use standard tools for dealing with the archived files by > looking using the underlying filesystem's mount point.
It's a mistake to think that snapshots are equivalent to archived files! While it is certainly a valid viewpoint if you only consider creating and deleting files, the two concepts become radically different if you consider modifying existing files.
--Stephen
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