rsync and MD5

Jeroen van der Vegt jeroen.van.der.vegt at
Tue Dec 16 14:05:53 GMT 2008

That decision obviously depends on processing power and network capacity
available. A recent thread on Slashdot
( mentioned this
research which might give more insight:

And btw, I though rsync used MD4, not MD5.

Jeroen van der Vegt	 
System designer 

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> -----Original Message-----
> From: at
> [ at]
> On Behalf Of David de Lama
> Sent: dinsdag 16 december 2008 14:34
> To: rsync at
> Subject: rsync and MD5
> Hi all!
> I've got a question about rsync using the MD5 algorithm.
> I know that rsync makes blocks of a file and then compares the checksums
> of each block.
> If the checksum is unequal the block is tranfered.
> Otherwise it could be that the checksum is the same but the block is
> different.
> Therefor rsync uses a 128 BIT MD5 algorithm.
> Now, at what filesize is it better to check the whole file with MD5 and
> when its faster just to copy the file?
> Is there a formula, table or diagram which it shows? (I think it depends
> on the Hardware!)
> Unfortunately I didn't find anything.
> Thanks a lot.
> Spanockel
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