[linux-lvm] read-only media in a LVM?
uzx87lvfmukwc001 at sneakemail.com
Mon Jun 23 16:23:01 UTC 2003
Sean P. Kane wrote 36 lines:
> Does a snapshot create a copy of all the files in memory?
Nope. And not in memory either.
> Just the files that changed?
Nope, LVM is filesystem-agnostic, and that would have to change
that. More code, more errors, less usability.
Additionally, what would you do with metadata, like used
filesystem blocks and timestamps and filenames?
Or with a 1 TB file where just 1 bit was changed?
> Or just the file blocks or contents (i.e. diffs) that have
Blocks of (default) 32Kb of raw disk. They are written to the
snapshot. However, the tables of which blocks were written are
kept in RAM, so a read request on the snapshot redirects only the
unchanged blocks to the original (HD/CD) and gets the changed
blocks out of the snapshot storage.
> So, would the snapshot have to be the same size as the cdrom or
> could it be smaller?
MUCH smaller. Unless you insist on changing something in every
32KB block of the CDrom.
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