On 4/26/07, Carlos E. R. <[EMAIL PROTECTED]> wrote:
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The Wednesday 2007-04-25 at 16:36 -0400, Greg Freemyer wrote:
> Neither of the solutions I posted earlier in this thread are dependent
> on timestamps.
>
> iirc: Especially for online backups rdiff-backup mentioned before
> ignores timestamps altogether. It calculates the MD5 for every file
> to see if any changes have been introduced. If they have it segments
> the file and drills down to find the smallest unit of change and only
> sends that data across the LAN/WAN.
I doubt that.
rdiff-backup is fast, and calculating MD5 for all files is slow. I think
it does that only for files it thinks that might have changed.
Proof:
Backing up my Mail list archive takes 4" right now. Calculating the
md5sums of one of the same dir takes 47" (37" on a second run).
Therefore, rdif. must be checking metadata instead.
Your right. My backup is also too fast to actually do a hash of every
file. My mistake.
I checked the man page and found:
--compare-hash: This is equivalent to '--compare-hash-at-time now'
--compare-hash-at-time time: Compare a directory with the backup set
at the given time. Regular files will be compared by computing their
SHA1 digest on the source side and comparing it to the digest recorded
in the metadata.
Or if you really want a byte-by-byte compare:
-compare-full: This is equivalent to '--compare-full-at-time now'
--compare-full-at-time time: Compare a directory with the backup set
at the given time. To compare regular files, the repository data will
be copied in its entirety to the source side and compared byte by
byte. This is the slowest but most complete compare option.
I did not experiment with any of these options, so I don't know if you
can simply add --compare_hash to a command line and get the backup
decision restructured via SHA1, or if the above are only ways to run a
verify pass.
Personally I'm fine with basing the first decision on MetaData, then
letting the rsync algorithm decide what exactly needs to be sent to
keep the primary and backup in sync.
Greg
--
Greg Freemyer
The Norcross Group
Forensics for the 21st Century
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