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Re: [linux-lvm] very slow fw performance when snapshots active


On 10/18/2007 10:39:50 AM +0200, Falko Zurell <falko zurell idmedia com> wrote:

Then I edit a 2 GB text file on /opt (XFS filesystem) with vi (just
hitting "enter" and save this minor change). This will take minutes to
finish the vi during saving.

This problem is not lvm-related: when opening a file with vim, it reads the entire file into memory (even if the file is 2GB), marks the changes into a .swp file. When saving, vim rewrites the entire file in place, effectively changing 2GB of copy on write blocks. This happens every time, with or without snapshot, the latter being worse because of the cow overhead.

for reading-only very large files, "less" or "more" read files on-demand which is a far more effecient way.

for writing, I don't know any method allowing to safely write a small change into a large file, except using awk or perl parsing (which reads the entire streamed file anyway)


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