Re:Kopia – Fast and Secure Open-Source Backup
by aidenn0 on Friday June 11, 2021 @02:55PM
(#27477162)
For local backups, compression is less of an issue; for things that are compressible, transparent file system compression seems to get about 110% the size of what I would get by any non-CPU bound levels of compression using a tgz. Since (as others in this thread have noted), compressible files tend to also be smaller files (the only exception I can think of would be if your log rotation doesn't compress old logs), the fact that only a fraction of what I backup is 10% larger is kind of "okay." When you're sending across the network though it can be a big deal.
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Re:Kopia – Fast and Secure Open-Source Backup
by MikusR on Friday June 11, 2021 @03:34PM
(#27477502)
On disk the backups are encrypted, that means no transparent compression.
Re:Kopia – Fast and Secure Open-Source Backup
by isbvhodnvemrwvn on Friday June 11, 2021 @04:33PM
(#27478126)
For people who haven't dealt with this - a good encryption scheme produces output which you can't tell apart from a purely random stream of bits - it has very high entropy, and is therefore not compressible.
Thanks for clarifying this. That must mean then: first encrypt, then compress?
Re:Kopia – Fast and Secure Open-Source Backup
by aidenn0 on Saturday June 12, 2021 @12:29AM
(#27481537)
Compress than encrypt.
Re:Kopia – Fast and Secure Open-Source Backup
by isbvhodnvemrwvn on Saturday June 12, 2021 @06:18AM
(#27483319)
And this has some pitfalls as well, ciphertext in general has about the same length as the plaintext, so compression rate can be used to infer some information about the plaintext. It's more of a problem with interactive protocols than with backups, but still worth keeping in mind.