Re: [PATCH 3/3] Add timeout feature

Pavel Machek
2008-07-13T12:05:28Z

Hi!

> NEED - provide way for SAN and hardware raid storage to do
> its snapshot/copy function while the system was in-use and
> get an image that could mount cleanly. Without freeze, at
> a minimum we usually needed filesystem metadata recovery
> to run, worst case is completely unusable snapshits :)
>
> freezefs() is single-level:
>
> ENOTSUPPOTED - by any other fs
> EOK - done
> EINPROGRESS
> EALREADY
>
> As implemented, freezefs only ensures the metadata is
> consistent so the filesystem copy can mount anywhere.
>
> This means ONLY SOME metadata (or no metadata) is flushed and
> then all metadata updates are stopped. User/kernel writes
> to already allocated file pages WILL go to a frozen disk.

That's the difference here. They do write file data, and thus avoid
mmap()-writes problem.

...and they _still_ provide auto-thaw.
Pavel
--
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