Craig Barratt wrote: > Rich writes: > > >> I don't think BackupPC will update the pool with the smaller file even >> though it knows the source was identical, and some tests I just did >> backing up /tmp seem to agree. Once compressed and copied into the >> pool, the file is not updated with future higher compressed copies. >> Does anyone know something otherwise? >> > > You're right. > > Each file in the pool is only compressed once, at the current > compression level. Matching pool files is done by comparing > uncompressed file contents, not compressed files. > > It's done this way because compression is typically a lot more > expensive than uncompressing. Changing the compression level > will only apply to new additions to the pool. > > To benchmark compression ratios you could remove all the files > in the pool between runs, but of course you should only do that > on a test setup, not a production installation. > > Craig > The other point to keep in mind is that unless you actually need compression for disk space reasons leaving it off will often be faster on a CPU bound server. Since there is a script provided (BackupPC_compressPool) to compress it later you can safely leave compression off until you need the disk space.
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